[media] uvcvideo: Return -EACCES when trying to access a read/write-only control

The proper return code according to the V4L2 specification is -EACCES,
not -EINVAL.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>