Fix the stereo microphone cache issue

Without this patch, we would not wipe the microphone cache after audio
is passed to audio framework. We would later use old cached data again.
This means we were sending data to audio framework too often causing
alsa mixer crashes.

Test: make a mono phone call, make stereo phone call, drop connection
during phone call, ensure no crashes and good audio quality
Bug: 209004829
Bug: 150670922
Change-Id: I07511439cb60ac8a772f523411fbca018cd3f995