fix(setup) Fix error when saving configuration step of setup

This was caused by the move of objectClass to plInfo is plugins.

issue #5880

setup/class_setupStepConfig.inc

@@ -42,6 +42,8 @@ class setupStepConfig extends configInLdap
   var $is_completed = FALSE;
   var $header_image;
 
+  protected $objectclasses = array('fusionDirectoryConf');
+
   static function plInfo()
   {
     return array();