ext/ffmpeg/gstffmpegcodecmap.c: Set property incompatible with DV demuxer so that it won't infinitely plug demuxers t...

Original commit message from CVS:
* ext/ffmpeg/gstffmpegcodecmap.c: (gst_ffmpeg_codecid_to_caps),
(gst_ffmpeg_caps_to_codecid):
Set property incompatible with DV demuxer so that it won't
infinitely plug demuxers to each other. Fixes playback of .dv
streams in Totem.