Fixed QtMultimedia core namespace compilation.

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

src/gsttools/qgstxvimagebuffer.cpp

@@ -50,6 +50,8 @@
 
 #ifndef QT_NO_XVIDEO
 
+QT_BEGIN_NAMESPACE
+
 GstBufferClass *QGstXvImageBuffer::parent_class = NULL;
 
 GType QGstXvImageBuffer::get_type(void)
@@ -307,5 +309,7 @@ void QGstXvImageBufferPool::destroyBuffer(QGstXvImageBuffer *xvBuffer)
         QMetaObject::invokeMethod(this, "queuedDestroy", Qt::QueuedConnection);
 }
 
+QT_END_NAMESPACE
+
 #endif //QT_NO_XVIDEO