LU-6096 ldiskfs: mark dir's inode dirty

mark directory's inode dirty in ldiskfs_add_dot_dotdot()
as ldiskfs_init_new_dir() doesn't do this internally.
otherwise, the attributes set by ldiskfs_append() aren't
transferred to the buffer cache.

Change-Id: Ice93b75e291736f83c0d9b1047f7a627fef0141e
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: http://review.whamcloud.com/15581
Tested-by: Jenkins
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>