Fixed QtMultimedia core namespace compilation.

Change-Id: Ie276a7766bd26f3e49b2bc9c1a28ec96f1e3e4b0
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.h

@@ -55,13 +55,13 @@
 
 #include <gst/gst.h>
 
+QT_BEGIN_NAMESPACE
+
 class QGstreamerBusHelper;
 class QGstreamerMessage;
 
 class QGstreamerVideoRendererInterface;
 
-QT_USE_NAMESPACE
-
 class QGstreamerPlayerSession : public QObject,
                                 public QGstreamerBusMessageFilter
 {
@@ -226,4 +226,6 @@ private:
     bool m_isLiveSource;
 };
 
+QT_END_NAMESPACE
+
 #endif // QGSTREAMERPLAYERSESSION_H