ptpclock: Fix error leak during failures
ptpclock: Fix error leak during failures

https://bugzilla.gnome.org/show_bug.cgi?id=755607

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