pylint: fix no-member in schema plugin
    
    The `module.register` member is added just a few lines
    before pylint warns there's none such thing.
    
    https://pagure.io/freeipa/issue/6874
    
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>