f2fs: do not set LOST_PINO for renamed dir

After renaming a directory, fsck could detect unmatched pino. The scenario
can be reproduced as the following:

	$ mkdir /bar/subbar /foo
	$ rename /bar/subbar /foo

Then fsck will report:
[ASSERT] (__chk_dots_dentries:1182)  --> Bad inode number[0x3] for '..', parent parent ino is [0x4]

Rename sets LOST_PINO for old_inode. However, the flag cannot be cleared,
since dir is written back with CP. So, let's get rid of LOST_PINO for a
renamed dir and fix the pino directly at the end of rename.
Signed-off-by: Sheng Yong <shengyong1@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/namei.c

@@ -772,7 +772,10 @@ static int f2fs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	}
 
 	down_write(&F2FS_I(old_inode)->i_sem);
-	file_lost_pino(old_inode);
+	if (!old_dir_entry || whiteout)
+		file_lost_pino(old_inode);
+	else
+		F2FS_I(old_inode)->i_pino = new_dir->i_ino;
 	up_write(&F2FS_I(old_inode)->i_sem);
 
 	old_inode->i_ctime = current_time(old_inode);