nullb: use blk_mq_alloc_disk

Use blk_mq_alloc_disk and blk_cleanup_disk to simplify the gendisk and
request_queue allocation.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Link: https://lore.kernel.org/r/20210602065345.355274-21-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk/main.c

@@ -1851,13 +1851,12 @@ static int null_add_dev(struct nullb_device *dev)
 
 		rv = -ENOMEM;
 		nullb->tag_set->timeout = 5 * HZ;
-		nullb->q = blk_mq_init_queue_data(nullb->tag_set, nullb);
-		if (IS_ERR(nullb->q))
+		nullb->disk = blk_mq_alloc_disk(nullb->tag_set, nullb);
+		if (IS_ERR(nullb->disk)) {
+			rv = PTR_ERR(nullb->disk);
 			goto out_cleanup_tags;
-		nullb->disk = alloc_disk_node(1, nullb->dev->home_node);
-		if (!nullb->disk)
-			goto out_cleanup_tags;
-		nullb->disk->queue = nullb->q;
+		}
+		nullb->q = nullb->disk->queue;
 	} else if (dev->queue_mode == NULL_Q_BIO) {
 		rv = -ENOMEM;
 		nullb->disk = blk_alloc_disk(nullb->dev->home_node);