Fix build with gcc <= 4.5

nullptr is not defined with gcc <= 4.5, use 0 instead.

Change-Id: I90d9170e57258f26b8ba7770a957a135539364de
Reviewed-by: Giulio Camuffo <giulio.camuffo@jollamobile.com>

src/compositor/compositor_api/qwaylandsurfaceview.cpp

@@ -69,7 +69,7 @@ QWaylandSurfaceView::~QWaylandSurfaceView()
     if (d->surface) {
         QWaylandInputDevice *i = d->surface->compositor()->defaultInputDevice();
         if (i->mouseFocus() == this)
-            i->setMouseFocus(nullptr, QPointF());
+            i->setMouseFocus(Q_NULLPTR, QPointF());
 
         d->surface->destroy();
         d->surface->d_func()->views.removeOne(this);