MDL-60658 course, gradebook: fix missing unformat_float for gradepass

Fix incorrect comparison of gradepass variable (with comma as decimal separator)
with grade variable when trying to save assignment settings.
Adds missing unformat_float($data['gradepass']).

course/moodleform_mod.php

@@ -408,7 +408,7 @@ abstract class moodleform_mod extends moodleform {
             } else {
                 $grade = $scale;
             }
-            if ($data['gradepass'] > $grade) {
+            if (unformat_float($data['gradepass']) > $grade) {
                 $errors['gradepass'] = get_string('gradepassgreaterthangrade', 'grades', $grade);
             }
         }