media: rkvdec: Do not require all controls to be present in every request

According to the v4l2 api, it is allowed to skip
setting a control if its contents haven't changed for performance
reasons: userspace should only update the controls that changed from
last frame rather then updating them all. Still some ancient code
that checks for mandatory controls has been left in this driver.

Remove it.

Fixes: cd33c830 ("media: rkvdec: Add the rkvdec driver")
Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>