gst/autodetect/: Post an error when we can't set the internal ghostpad target.

gst/autodetect/: Post an error when we can't set the internal ghostpad target.

Original commit message from CVS:
* gst/autodetect/gstautoaudiosink.c: (gst_auto_audio_sink_detect):
* gst/autodetect/gstautoaudiosrc.c: (gst_auto_audio_src_detect):
* gst/autodetect/gstautovideosink.c: (gst_auto_video_sink_reset),
(gst_auto_video_sink_detect):
* gst/autodetect/gstautovideosrc.c: (gst_auto_video_src_detect):
Post an error when we can't set the internal ghostpad target.