Help Search: Fix re-index button

The re-index button was connected to the wrong help search engine.

Change-Id: I945853886a8cb0462eef71d22c48a1ac92c1eec1
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/help/searchwidget.h

@@ -72,6 +72,10 @@ public:
     void zoomOut();
     void resetZoom();
 
+
+public slots:
+    void reindexDocumentation();
+
 signals:
     void linkActivated(const QUrl &link, bool newPage);