[AE/osxsink] - fix possible device changed loop when using passthrough

Damnit - that one slipped in when i added the registration to the default output device changed callback.

@jmarshalnz for review - Gotham material sadly.
Thanks.  Is there any possibility we can detect what is going on in 3 and 4?  Do we need to re-enumerate if all that is happened is the default output device is changed (as I presume we're not using that device here?)