drm/amd/display: fix null pointer deref error

drm/amd/display: fix null pointer deref error

[Why]
0 was passed in place of a pointer which triggered null pointer
dereference.

Causes a backtrace like:

[   41.159466] RIP: 0010:dccg31_set_audio_dtbclk_dto+0x10/0x120 [amdgpu]
[   41.159928] Code: c0 00 00 00 6a 01 8b 92 84 01 00 00 52 0f b6 40 61 e9 30 ff ff ff 0f 1f 40 00 0f 1f 44 00 00 55 48 89 e5 41 56 41 55 41 54 53 <44> 8b 66 18 48 89 fb 48 8b 47 30 48 8b 3f 45 85 e4 74 09 4c 63 6e
[   41.159932] RSP: 0018:ffffaee54055afd0 EFLAGS: 00010246
[   41.159936] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff917445901800
[   41.159939] RDX: ffffffffc15e6ca0 RSI: 0000000000000000 RDI: ffff91744dbd8c60
[   41.159941] RBP: ffffaee54055aff0 R08: 0000000000000100 R09: ffffaee54055afe8
[   41.159944] R10: 0000000000000001 R11: 0000000000000009 R12: ffff91747ca201f0
[   41.159946] R13: ffff91747ca20000 R14: ffff917448720438 R15: ffff91747ca20000
[   41.159948] FS:  00007f5e13e5f740(0000) GS:ffff91775ca40000(0000) knlGS:0000000000000000
[   41.159951] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   41.159954] CR2: 0000000000000018 CR3: 000000010fea0000 CR4: 00000000003506e0
[   41.159956] Call Trace:
[   41.159959]  <TASK>
[   41.159964]  dce110_setup_audio_dto.isra.0+0xd8/0x1f0 [amdgpu]
[   41.160411]  dce110_apply_ctx_to_hw+0x1aa/0x780 [amdgpu]
[   41.160842]  ? __free_pages+0x88/0xb0
[   41.160850]  ? kfree+0x360/0x3e0
[   41.160857]  dc_commit_state+0x337/0xac0 [amdgpu]
[   41.161135]  amdgpu_dm_atomic_commit_tail+0x5e3/0x2680 [amdgpu]

[How]
Pass in a pointer that contains nullified parameters instead of null
pointer.

Fixes: 405bb9eea36a ("drm/amd/display: Implement DTBCLK ref switching on dcn32")
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>