block: remove the extra kobject reference in bd_link_disk_holder

Since commit 0d02129e ("block: merge struct block_device and struct
hd_struct") there is no way for the bdev to go away as long as there is
a holder, so remove the extra references.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Link: https://lore.kernel.org/r/20210804094147.459763-3-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/holder.c

@@ -92,11 +92,6 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	ret = add_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
 	if (ret)
 		goto out_del;
-	/*
-	 * bdev could be deleted beneath us which would implicitly destroy
-	 * the holder directory.  Hold on to it.
-	 */
-	kobject_get(bdev->bd_holder_dir);
 
 	list_add(&holder->list, &bdev->bd_holder_disks);
 	goto out_unlock;
@@ -130,7 +125,6 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
 		del_symlink(disk->slave_dir, bdev_kobj(bdev));
 		del_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
-		kobject_put(bdev->bd_holder_dir);
 		list_del_init(&holder->list);
 		kfree(holder);
 	}