block: fix checking return value of blk_mq_init_queue

Check IS_ERR_OR_NULL(return value) instead of just return value.
Signed-off-by: NMing Lei <ming.lei@canonical.com>

Reduced to IS_ERR() by me, we never return NULL.
Signed-off-by: NJens Axboe <axboe@fb.com>

drivers/block/null_blk.c

@@ -530,7 +530,7 @@ static int null_add_dev(void)
 			goto out_cleanup_queues;
 
 		nullb->q = blk_mq_init_queue(&nullb->tag_set);
-		if (!nullb->q) {
+		if (IS_ERR(nullb->q)) {
 			rv = -ENOMEM;
 			goto out_cleanup_tags;
 		}

drivers/block/nvme-core.c

@@ -1376,7 +1376,7 @@ static int nvme_alloc_admin_tags(struct nvme_dev *dev)
 			return -ENOMEM;
 
 		dev->admin_q = blk_mq_init_queue(&dev->admin_tagset);
-		if (!dev->admin_q) {
+		if (IS_ERR(dev->admin_q)) {
 			blk_mq_free_tag_set(&dev->admin_tagset);
 			return -ENOMEM;
 		}

drivers/block/virtio_blk.c

@@ -638,7 +638,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 		goto out_put_disk;
 
 	q = vblk->disk->queue = blk_mq_init_queue(&vblk->tag_set);
-	if (!q) {
+	if (IS_ERR(q)) {
 		err = -ENOMEM;
 		goto out_free_tags;
 	}