hpfs: update ctime and mtime on directory modification

Update ctime and mtime when a directory is modified. (though OS/2 doesn't
update them anyway)

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@kernel.org	# v3.3+
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>