media: rockchip/vpu: Get vdev from the file arg in vidioc_querycap()

This makes the function more generic so it can easily be re-used when
adding support for the decoding functionality.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>