osxaudio: Clean up a GstCoreAudio -> GstOsxAudioSrc/Sink reference

Now that device selection has no sink/source-specific bits, we can have
generic device selection for this path. We do need to now track state
changes so we can look up the final device_id once the device is open,
though.

https://bugzilla.gnome.org/show_bug.cgi?id=740987
8 files changed