audio: Add callback event to asynchronously notify error

Add new event to notify error using async callback path

Change-Id: I80a0ff74ea5a6497331a87ee33b2d0a890cbd2db
diff --git a/include/hardware/audio.h b/include/hardware/audio.h
index 36bfa86..ec7fd4b 100644
--- a/include/hardware/audio.h
+++ b/include/hardware/audio.h
@@ -253,7 +253,8 @@
 /* type of asynchronous write callback events. Mutually exclusive */
 typedef enum {
     STREAM_CBK_EVENT_WRITE_READY, /* non blocking write completed */
-    STREAM_CBK_EVENT_DRAIN_READY  /* drain completed */
+    STREAM_CBK_EVENT_DRAIN_READY,  /* drain completed */
+    STREAM_CBK_EVENT_ERROR, /* stream hit some error, let AF take action */
 } stream_callback_event_t;
 
 typedef int (*stream_callback_t)(stream_callback_event_t event, void *param, void *cookie);