[media] uvcvideo: Don't stop the stream twice at file handle release

When releasing the file handle the driver calls the vb2_queue_release
which turns the stream off. There's thus no need to turn the stream off
explicitly beforehand.

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