V4L/DVB (13152): uvcvideo: Rely on videodev to reference-count the device

The uvcvideo driver has a driver-wide lock and a reference count to protect
against a disconnect/open race. Now that videodev handles the race itself,
reference-counting in the driver can be removed.

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