Switch to use audio usage instead of stream_type in Car Settings UI

This CL changes nothing but method name. A following CL should either
remove or refactor the CarVolumeDialogController class as we are moving
to use AudioAttributes usage instead of stream_type.

Bug: 28469751
Test: lunch bat_land-userdebug && m -j // Then flash and open the app
Change-Id: Ic3c657ed36d67fbbc18b6787b04bff147ee693a2