Fix AudioSystem::getAudioPort implementation

The implementation used to try to convert the complete provided
audio port into AIDL before passing to AP Service. The
corresponding AP Service method has been changed to only take
the port ID—the only piece of information which is actually
used by APM.

Bug: 221075345
Test: in preparation by a contractor
Change-Id: Id274ee14a8bfd2dcbfbb22b7a09b89dc6b7314ce