FS#13996: Have audio_hard_stop() kill the PCM output path entirely

We already shut down the playback path and the voice path, but that
doesn't necessarily mean the PCM hardware is idle.

Add a call to pcm_play_stop() to ensure the PCM sink is completely idle.
This will prevent a badly-timed callback from firing during a ROLO
operation.

Change-Id: I1eb8c105895fb47bc3d0af91b4d87345f5399aa4

apps/playback.c

@@ -27,6 +27,7 @@
 #include "core_alloc.h"
 #include "sound.h"
 #include "pcm_sink.h"
+#include "pcm-internal.h"
 #include "codecs.h"
 #include "codec_thread.h"
 #include "voice_thread.h"
@@ -3996,8 +3997,11 @@ void audio_hard_stop(void)
     LOGFQUEUE("audio >| audio Q_AUDIO_STOP: 1");
     audio_queue_send(Q_AUDIO_STOP, 1);
 #ifdef PLAYBACK_VOICE
+    /* Stop voice */
     voice_stop();
 #endif
+    /* Stop PCM */
+    pcm_play_stop();
     audiobuf_handle = core_free(audiobuf_handle);
 }