Fixed QtMultimedia core namespace compilation.

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

src/plugins/gstreamer/qx11videosurface.h

@@ -51,7 +51,7 @@
 #include <X11/extensions/Xv.h>
 #include <X11/extensions/Xvlib.h>
 
-QT_USE_NAMESPACE
+QT_BEGIN_NAMESPACE
 
 class QX11VideoSurface : public QAbstractVideoSurface
 {
@@ -112,6 +112,8 @@ private:
     static int redistribute(int value, int fromLower, int fromUpper, int toLower, int toUpper);
 };
 
+QT_END_NAMESPACE
+
 #endif //QT_NO_XVIDEO
 
 #endif