rbd: drop needless test in rbd_rq_fn()

There's a test for null rq pointer inside the while loop in
rbd_rq_fn() that's not needed.  That same test already occurred
in the immediatly preceding loop condition test.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>

drivers/block/rbd.c

@@ -1475,10 +1475,6 @@ static void rbd_rq_fn(struct request_queue *q)
 		struct rbd_req_coll *coll;
 		struct ceph_snap_context *snapc;
 
-		/* peek at request from block layer */
-		if (!rq)
-			break;
-
 		dout("fetched request\n");
 
 		/* filter out block requests we don't understand */