[media] uvcvideo: remove unneeded access_ok() check

copy_in_user() already checks for write permission, so we don't need to
do it here.  This was added in 1a5e4c867c "[media] uvcvideo: Implement
compat_ioctl32 for custom ioctls".

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>