harness: fix compilation
harness: fix compilation

Was supposed to be squashed with 336c7bb6

https://bugzilla.gnome.org/show_bug.cgi?id=761910

StreamUtils/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,centricular/gstreamer,centricular/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer