Ios: Add missing "override" modifiers.

Change-Id: I9d57222f86af8ecbdc0d6d7969c14da523a198be
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/ios/iosdeploystep.h

@@ -73,7 +73,7 @@ public:
 
     void run(QFutureInterface<bool> &fi) override;
     void cleanup();
-    void cancel();
+    void cancel() override;
 signals:
     //void done();
     //void error();