mmc: vub300: replace deprecated strncpy with strscpy

mmc: vub300: replace deprecated strncpy with strscpy

`strncpy` is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect `vub300->vub_name` to be NUL-terminated based on its uses with
format strings:
| 	dev_info(&vub300->udev->dev, "using %s for SDIO offload processing\n",
| 		 vub300->vub_name);

NUL-padding is not needed. We can see cleaning out vub_name simply
consists of:
|       vub300->vub_name[0] = 0;

Considering the above, for all 11 cases a suitable replacement is
`strscpy` [2] due to the fact that it guarantees NUL-termination on the
destination buffer without unnecessarily NUL-padding.

To be clear, there is no existing bug in the current implementation as
the string literals are all small enough as to not cause a buffer
overread. Nonetheless, this gets us 11 steps closer to removing strncpy
uses.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20230927-strncpy-drivers-mmc-host-vub300-c-v1-1-77426f62eef4@google.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>