MDL-26523 grade: fixed a called to addHelpButton() that was asking fo…

…r a non-existent string

grade/edit/tree/grade_form.php

@@ -80,7 +80,7 @@ function definition() {
             }
 
             $mform->addElement('select', 'finalgrade', get_string('finalgrade', 'grades'), $scaleopt);
-            $mform->addHelpButton('finalgrade', 'finalgrade', 'finalgrade');
+            $mform->addHelpButton('finalgrade', 'finalgrade', 'grades');
             $mform->disabledIf('finalgrade', 'overridden', 'notchecked');
         }