[media] uvc: Add return code check at vb2_queue_init()

This function returns an integer and it's mandatory
to check the return code.

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