[PATCH] AS buglet

This one won't cause hangs, but can trip some WARNs.

drivers/block/as-iosched.c

@@ -1610,6 +1610,7 @@ static void as_merged_request(request_queue_t *q, struct request *req)
 		 */
 	}
 
+	if (arq->on_hash)
 		q->last_merge = req;
 }