media: mtk-vcodec: potential null pointer deference in SCP

The return value of devm_kzalloc() needs to be checked to avoid
NULL pointer deference. This is similar to CVE-2022-3113.

Link: https://lore.kernel.org/linux-media/PH7PR20MB5925094DAE3FD750C7E39E01BF712@PH7PR20MB5925.namprd20.prod.outlook.com


Signed-off-by: Fullway Wang <fullwaywang@outlook.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>