Typos from Drupal 7 conversion

There are a couple of leftovers from the D7 version where bat_unit_bundles_ids() and UnitType::getEventValueFormatter() use the ->label property directly, and bat_type_access_filter() uses $op instead of $operation.

I don't consider the last one a security issue since $op would always be undefined, and if anything actually called bat_type_access_filter() it would always be considered an invalid/denied operation.