hal: fix trailing sound heard during a2dp codec switch

When a2dp reconfig comes for pcm offload usecase, path
can be disabled without switching to speaker, which
leads cached PCM data rendered out after switching to
new codec, so trailing sound can be heard first and then
followed with mute, and finally when unmute is issued,
the mute period can sound like a glitch.

Change-Id: I8dc4349d0cb334252f1f9bbb27713e71a0bc7fb3