drm/amdgpu: Fix 'fw_name' buffer size to prevent truncations in amdgpu_mes_init_microcode

drm/amdgpu: Fix 'fw_name' buffer size to prevent truncations in amdgpu_mes_init_microcode

The snprintf function is used to write a formatted string into fw_name.
The format of the string is "amdgpu/%s_mes%s.bin", where %s is replaced
by the string in ucode_prefix and the second %s is replaced by either
"_2" or "1" depending on the condition pipe == AMDGPU_MES_SCHED_PIPE.

The length of the string "amdgpu/%s_mes%s.bin" is 16 characters plus the
length of ucode_prefix and the length of the string "_2" or "1". The
size of ucode_prefix is 30, so the maximum length of ucode_prefix is 29
characters (since one character is needed for the null terminator).
Therefore, the maximum possible length of the string written into
fw_name is 16 + 29 + 2 = 47 characters.

The size of fw_name is 40, so if the length of the string written into
fw_name is more than 39 characters (since one character is needed for
the null terminator), it will be truncated by the snprintf function, and
thus warnings will be seen.

By increasing the size of fw_name to 50, we ensure that fw_name is
large enough to hold the maximum possible length of the string, so the
snprintf function will not truncate the output.

Fixes the below with gcc W=1:
drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c: In function ‘amdgpu_mes_init_microcode’:
drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c:1482:66: warning: ‘%s’ directive output may be truncated writing up to 1 bytes into a region of size between 0 and 29 [-Wformat-truncation=]
 1482 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_mes%s.bin",
      |                                                                  ^~
drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c:1482:17: note: ‘snprintf’ output between 16 and 46 bytes into a destination of size 40
 1482 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_mes%s.bin",
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 1483 |                          ucode_prefix,
      |                          ~~~~~~~~~~~~~
 1484 |                          pipe == AMDGPU_MES_SCHED_PIPE ? "" : "1");
      |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c:1477:66: warning: ‘%s’ directive output may be truncated writing 1 byte into a region of size between 0 and 29 [-Wformat-truncation=]
 1477 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_mes%s.bin",
      |                                                                  ^~
 1478 |                          ucode_prefix,
 1479 |                          pipe == AMDGPU_MES_SCHED_PIPE ? "_2" : "1");
      |                                                                 ~~~
drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c:1477:17: note: ‘snprintf’ output between 17 and 46 bytes into a destination of size 40
 1477 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_mes%s.bin",
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 1478 |                          ucode_prefix,
      |                          ~~~~~~~~~~~~~
 1479 |                          pipe == AMDGPU_MES_SCHED_PIPE ? "_2" : "1");
      |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c:1477:66: warning: ‘%s’ directive output may be truncated writing 2 bytes into a region of size between 0 and 29 [-Wformat-truncation=]
 1477 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_mes%s.bin",
      |                                                                  ^~
 1478 |                          ucode_prefix,
 1479 |                          pipe == AMDGPU_MES_SCHED_PIPE ? "_2" : "1");
      |                                                          ~~~~
drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c:1477:17: note: ‘snprintf’ output between 18 and 47 bytes into a destination of size 40
 1477 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_mes%s.bin",
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 1478 |                          ucode_prefix,
      |                          ~~~~~~~~~~~~~
 1479 |                          pipe == AMDGPU_MES_SCHED_PIPE ? "_2" : "1");
      |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c:1489:62: warning: ‘_mes.bin’ directive output may be truncated writing 8 bytes into a region of size between 4 and 33 [-Wformat-truncation=]
 1489 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_mes.bin",
      |                                                              ^~~~~~~~
drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c:1489:17: note: ‘snprintf’ output between 16 and 45 bytes into a destination of size 40
 1489 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_mes.bin",
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 1490 |                          ucode_prefix);
      |                          ~~~~~~~~~~~~~

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Suggested-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>