modify close sample code

Signed-off-by: Nlixiang <lixiang380@huawei.com>

zh-cn/application-dev/reference/apis/js-apis-webview.md

@@ -81,7 +81,7 @@ import web_webview from '@ohos.web.webview'
 @Component
 struct WebComponent {
   controller: web_webview.WebviewController = new web_webview.WebviewController();
-  msgPort: WebMessagePort[] = null;
+  msgPort: web_webview.WebMessagePort[] = null;
 
   build() {
     Column() {