Don't release focus until all audio ops are done

In Telecom, don't release audio focus until we finish doing everything
we need to do with the audio stack -- if we release focus early, we risk
conflicting with other apps that start doing stuff.

Fixes: 139868627
Test: atest CallAudioModeTransitionTests, manual
Change-Id: Ibba6c357c8a308e5883ebd81cb9464b9fec905c7