blk-mq: fix allocation of set->tags

type of set->tags is struct blk_mq_tags **.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NMing Lei <tom.leiming@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

block/blk-mq.c

@@ -1537,7 +1537,8 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
 		return -EINVAL;
 
 
-	set->tags = kmalloc_node(set->nr_hw_queues * sizeof(struct blk_mq_tags),
+	set->tags = kmalloc_node(set->nr_hw_queues *
+				 sizeof(struct blk_mq_tags *),
 				 GFP_KERNEL, set->numa_node);
 	if (!set->tags)
 		goto out;