audio:sst: Flush message reply wq before allowing runtime suspend to exit

audio:sst: Flush message reply wq before allowing runtime suspend to exit

BZ: 32221

Audio IPC message processing happens in a workqueue while the runtime
suspend in running in different context. There is a race condition
between those. Sometimes runtime suspend turns the audio sub system off
before the message workqueue is finished. At the end of the
message handling there are writes to audio sub system registers.

Flush the message handling workqueues before leaving the runtime_suspend
call. This guarantees that the other activity is properly finished.

Change-Id: I1612fb3206a186b0877f0c8dc94bf0ee40c9dfe5
Signed-off-by: Samu Onkalo <samu.onkalo@intel.com>
Signed-off-by: Ramesh Babu K V <ramesh.babu@intel.com>
Reviewed-on: http://android.intel.com:8080/49229
Reviewed-by: Koskinen, Ilkka <ilkka.koskinen@intel.com>
Reviewed-by: Koul, Vinod <vinod.koul@intel.com>
Reviewed-by: Gupta, ArvindX K <arvindx.k.gupta@intel.com>
Reviewed-by: Hibare, PramodX <pramodx.hibare@intel.com>
Tested-by: Hibare, PramodX <pramodx.hibare@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>