elevator: fix double release of elevator module

Our issue is descripted in below call path:
->elevator_init
 ->elevator_init_fn
  ->{cfq,deadline,noop}_init_queue
   ->elevator_alloc
    ->kzalloc_node
   fail to call kzalloc_node and then put module in elevator_alloc;
fail to call elevator_init_fn and then put module again in elevator_init.

Remove elevator_put invoking in error path of elevator_alloc to avoid
double release issue.
Signed-off-by: NChao Yu <chao2.yu@samsung.com>
Reviewed-by: NJeff Moyer <jmoyer@redhat.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

block/elevator.c

@@ -157,7 +157,7 @@ struct elevator_queue *elevator_alloc(struct request_queue *q,
 
 	eq = kzalloc_node(sizeof(*eq), GFP_KERNEL, q->node);
 	if (unlikely(!eq))
-		goto err;
+		return NULL;
 
 	eq->type = e;
 	kobject_init(&eq->kobj, &elv_ktype);
@@ -165,10 +165,6 @@ struct elevator_queue *elevator_alloc(struct request_queue *q,
 	hash_init(eq->hash);
 
 	return eq;
-err:
-	kfree(eq);
-	elevator_put(e);
-	return NULL;
 }
 EXPORT_SYMBOL(elevator_alloc);