media: platform: mediatek: vpu: fix NULL ptr dereference

If pdev is NULL, then it is still dereferenced.

This fixes this smatch warning:

drivers/media/platform/mediatek/vpu/mtk_vpu.c:570 vpu_load_firmware() warn: address of NULL pointer 'pdev'

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Yunfei Dong <yunfei.dong@mediatek.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>