f2fs: fix i_name during f2fs_sync_file

As similar as the i_pino fix, i_name also should be fixed when i_nlink is 1.

The errorneous scenario is like this.

1. touch test1
2. link test1 test2
3. unlink test2
4. fsync test1

After this, i_name should be test1.

CC: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/file.c

@@ -112,11 +112,13 @@ static int get_parent_ino(struct inode *inode, nid_t *pino)
 	if (!dentry)
 		return 0;
 
-	inode = igrab(dentry->d_parent->d_inode);
-	dput(dentry);
+	if (update_dent_inode(inode, &dentry->d_name)) {
+		dput(dentry);
+		return 0;
+	}
 
-	*pino = inode->i_ino;
-	iput(inode);
+	*pino = parent_ino(dentry);
+	dput(dentry);
 	return 1;
 }