Fix the build error in public headers

One should always use Q_SLOTS/Q_SIGNALS in then public headers

Change-Id: Ibbba0d3ff402bd320049bcd58ced07ad1342ef3b
Reviewed-by: Giulio Camuffo <giulio.camuffo@jollamobile.com>

src/compositor/compositor_api/qwaylandsurface.h

@@ -227,7 +227,7 @@ public:
 
     static QWaylandSurface *fromResource(::wl_resource *resource);
 
-public slots:
+public Q_SLOTS:
     void updateSelection();
 
 protected:

src/compositor/compositor_api/qwaylandsurfaceitem.h

@@ -102,11 +102,11 @@ protected:
     void touchEvent(QTouchEvent *event);
     void mouseUngrabEvent() Q_DECL_OVERRIDE;
 
-public slots:
+public Q_SLOTS:
     virtual void takeFocus(QWaylandInputDevice *device = 0);
     void setPaintEnabled(bool paintEnabled);
 
-private slots:
+private Q_SLOTS:
     void surfaceMapped();
     void surfaceUnmapped();
     void parentChanged(QWaylandSurface *newParent, QWaylandSurface *oldParent);