blk-mq: Fix memory leak in error handling

If blk_mq_init_allocated_queue() fails, make sure to free the poll
stat callback struct allocated.
Signed-off-by: Jes Sorensen <jsorensen@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -2865,7 +2865,7 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 		goto err_exit;
 
 	if (blk_mq_alloc_ctxs(q))
-		goto err_exit;
+		goto err_poll;
 
 	/* init q->mq_kobj and sw queues' kobjects */
 	blk_mq_sysfs_init(q);
@@ -2929,6 +2929,9 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 	kfree(q->queue_hw_ctx);
 err_sys_init:
 	blk_mq_sysfs_deinit(q);
+err_poll:
+	blk_stat_free_callback(q->poll_cb);
+	q->poll_cb = NULL;
 err_exit:
 	q->mq_ops = NULL;
 	return ERR_PTR(-ENOMEM);