Reset last known audio state upon losing audio focus

mLastKnownCallAudioState is checked before triggering
notification to the rest of the framework. Not resetting
this variable upon losing the audio focus results in
not sending notification to the framework later.
This commit resets mLastKnownCallAudioState during
re-initialization of the state machine.

BUG=28642858

Change-Id: I8740c4c55a523cedf1e9aba1bf1c55fdda94dd1b