block: Fix an error handling in add_partition

Once we have called device_initialize(), we should use put_device() to
give up the reference on error, just like what we have done on failure
of device_add().
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/partitions/core.c

@@ -384,7 +384,7 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 
 	err = blk_alloc_devt(bdev, &devt);
 	if (err)
-		goto out_bdput;
+		goto out_put;
 	pdev->devt = devt;
 
 	/* delay uevent until 'holders' subdir is created */