block: bd_start_claiming fix module refcount

bd_start_claiming has an unbalanced module_put introduced in 6b4517a79.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

fs/block_dev.c

@@ -734,6 +734,7 @@ static struct block_device *bd_start_claiming(struct block_device *bdev,
 		return ERR_PTR(-ENXIO);
 
 	whole = bdget_disk(disk, 0);
+	module_put(disk->fops->owner);
 	put_disk(disk);
 	if (!whole)
 		return ERR_PTR(-ENOMEM);