f2fs: remove rename and use rename2

Refer the following patch.

commit 7177a9c4
Author: Miklos Szeredi <mszeredi@suse.cz>
Date:   Wed Jul 23 15:15:30 2014 +0200

    fs: call rename2 if exists

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>