Fixed QtMultimedia core namespace compilation.

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

src/plugins/gstreamer/mediacapture/qgstreamerv4l2input.h

@@ -49,7 +49,7 @@
 #include <QtCore/qsize.h>
 #include "qgstreamercapturesession.h"
 
-QT_USE_NAMESPACE
+QT_BEGIN_NAMESPACE
 
 class QGstreamerV4L2Input : public QObject, public QGstreamerVideoInput
 {
@@ -80,4 +80,6 @@ private:
     QByteArray m_device;
 };
 
+QT_END_NAMESPACE
+
 #endif // QGSTREAMERV4L2INPUT_H