ext2: also update the inode on disk when dir is IS_DIRSYNC

We used to just write changed page for IS_DIRSYNC inodes.  But we also
have to update the directory inode itself just for the case that we've
allocated a new block and changed i_size.

[akpm@linux-foundation.org: still sync the data page]
Signed-off-by: Jan Kara <jack@suse.cz>
Tested-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>