block: fix wrong error return in elevator_init()

while compiling integer err was showing as a set but unused variable.
elevator_init_fn can be either cfq_init_queue or deadline_init_queue
or noop_init_queue.
all three of these functions are returning -ENOMEM if they fail to
allocate the queue.
so we should actually be returning the error code rather than
returning 0 always.
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/elevator.c

@@ -229,7 +229,9 @@ int elevator_init(struct request_queue *q, char *name)
 	}
 
 	err = e->ops.elevator_init_fn(q, e);
-	return 0;
+	if (err)
+		elevator_put(e);
+	return err;
 }
 EXPORT_SYMBOL(elevator_init);