fix variable credit validation

src/app/dars/new-degree-audit-dialog/new-degree-audit-dialog.component.html

@@ -134,7 +134,10 @@
               </label>
               <mat-form-field>
                 <mat-label>{{ course.creditMin }}-{{ course.creditMax }} cr</mat-label>
-                <mat-select attr.aria-label="{{ credit }} credits" formControlName="credits" aria-labelledby="credits-range-{{ course.id }}" aria-labelledby="credits-range-{{ course.id }}">
+                <mat-select
+                  formControlName="creditsDropdown"
+                  attr.aria-label="{{ credit }} credits"
+                  aria-labelledby="credits-range-{{ course.id }}">
                   <mat-option
                     attr.aria-label="{{ credit }} credits"
                     *ngFor="let credit of course.range"