docs: def _get_firmware_update_element(self):
          """Get the url for firmware update
  
          :returns: firmware update url
          :raises: Missing resource error on missing url
          """
          fw_update_action = self._actions.update_firmware
          if not fw_update_action:
              raise (sushy.exceptions.
                     MissingActionError(action='#UpdateService.SimpleUpdate',
                                        resource=self._path))
          return fw_update_action