site switch bug fixed

lib/modules/demo_module/create_demo_request_page.dart

@@ -246,6 +246,9 @@ class _CreateDemoRequestPageState extends State<CreateDemoRequestPage> with Tick
         showAsBottomSheet: true,
         onSelect: (value) {
           _demoFormModel.site = value;
+          _demoFormModel.building = null;
+          _demoFormModel.floor = null;
+          _demoFormModel.department = null;
           setState(() {});
         },
       ),