Fix MSVC compiler warning.

class/struct mismatch.

Change-Id: Ifaecc4ba4baeceb41fffba84678466faf48469bc
Reviewed-on: http://codereview.qt.nokia.com/2156
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>

src/gui/kernel/qplatformscreen_qpa.cpp

@@ -46,8 +46,9 @@
 #include <QtGui/qscreen.h>
 #include <QtGui/qwindow.h>
 
-struct QPlatformScreenPrivate
+class QPlatformScreenPrivate
 {
+public:
     QScreen *screen;
 };