Btrfs: update directory's size when creating subvol/snapshot

Make sure directory's size properly updated when creating
subvol/snapshot.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 4604178..4e7b56e 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -819,6 +819,10 @@
 	if (ret)
 		goto fail;
 
+	btrfs_i_size_write(parent_inode, parent_inode->i_size + namelen * 2);
+	ret = btrfs_update_inode(trans, parent_root, parent_inode);
+	BUG_ON(ret);
+
 	/* add the backref first */
 	ret = btrfs_add_root_ref(trans, parent_root->fs_info->tree_root,
 				 pending->root_key.objectid,