Fix correct variable value

Setting "drh_autosubscribe" exists but "DRH_autosubscribe" doesn't.

main/inc/lib/events.lib.php

@@ -83,7 +83,7 @@ class Event
         Database::query($sql);
 
         // Auto subscribe
-        $user_status = $userInfo['status'] == SESSIONADMIN ? 'sessionadmin' : $userInfo['status'] == COURSEMANAGER ? 'teacher' : $userInfo['status'] == DRH ? 'DRH' : 'student';
+        $user_status = $userInfo['status'] == SESSIONADMIN ? 'sessionadmin' : $userInfo['status'] == COURSEMANAGER ? 'teacher' : $userInfo['status'] == DRH ? 'drh' : 'student';
         $autoSubscribe = api_get_setting($user_status.'_autosubscribe');
         if ($autoSubscribe) {
             $autoSubscribe = explode('|', $autoSubscribe);