[media] uvcvideo: Convert to unlocked_ioctl

The uvcvideo driver now locks all ioctls correctly on its own, the BKL
isn't needed anymore.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>