GStreamer: fix memory leaks.

Many GStreamer objects were not properly managed or never released.

Change-Id: I38b3854e8b9e2264b5b647f331d3bb16b886e2d6
Reviewed-by: Andrew den Exter <andrew.den.exter@qinetic.com.au>

src/plugins/gstreamer/mediacapture/qgstreameraudioencode.cpp

@@ -196,6 +196,8 @@ GstElement *QGstreamerAudioEncode::createEncoder()
         //qDebug() << "set caps filter:" << gst_caps_to_string(caps);
 
         g_object_set(G_OBJECT(capsFilter), "caps", caps, NULL);
+
+        gst_caps_unref(caps);
     }
 
     if (encoderElement) {