omxaudiodec: use default pad accept-caps handling
omxaudiodec: use default pad accept-caps handling

Instead of the audiodecoder one. The OMX audioo decoders have their
valid input in the template pad, so just check against that to
avoid doing a query downstream.

GStreamer/gst-omx,CapOM/gst-omx,CapOM/gst-omx,GStreamer/gst-omx,varunkumara/test-repo,varunkumara/test-repo,varunkumara/test-repo,CapOM/gst-omx,GStreamer/gst-omx