QAndroidPlatformScreen: Add missing override

Missed in b018a5ecef.

Reported-by: Anton Kudryavtsev <antkudr@mail.ru>
Change-Id: Id833fbd77c571923571e59b0c609b56c69308d90
Reviewed-by: BogDan Vatra <bogdan@kdab.com>
Reviewed-by: Anton Kudryavtsev <antkudr@mail.ru>

src/plugins/platforms/android/qandroidplatformscreen.h

@@ -89,7 +89,7 @@ public slots:
     void setSize(const QSize &size);
 
 protected:
-    bool event(QEvent *event);
+    bool event(QEvent *event) override;
 
     typedef QList<QAndroidPlatformWindow *> WindowStackType;
     WindowStackType m_windowStack;