change test to slider for disk create

app/UI/Disk/Forms/UpdateForm.php

@@ -43,14 +43,14 @@ class UpdateForm extends BaseForm implements ClientArea
         $this->setProvider(new DiskProvider());
         $this->initFields();
         $this->loadDataToForm();
-        $this->minSize = parent::getFormData('size');
+        $this->minSize = parent::getFormData()['size'];
 
         logModuleCall(
             'proxmoxCloud',
             __FUNCTION__,
-            parent::getFormData('id'),
+            parent::getFormData()['id'],
             'Debug',
-            parent::getFormData('size')
+            parent::getFormData()['size']
         );
 
     }