pam_winbind: fix comment typos

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Martin Schwenke <martin@meltin.net>

Autobuild-User(master): Martin Schwenke <martins@samba.org>
Autobuild-Date(master): Sat Oct 18 12:41:07 CEST 2014 on sn-devel-104