Use AudioTrack::event_type not int in callback

Change-Id: Ifefc708d46874e04fd0d01cb6e2d43b987ee796c
diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index df30e8c..4fc7f2d 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -99,7 +99,7 @@
      *          - EVENT_BUFFER_END: unused.
      */
 
-    typedef void (*callback_t)(int event, void* user, void *info);
+    typedef void (*callback_t)(event_type event, void* user, void *info);
 
     /* Returns the minimum frame count required for the successful creation of
      * an AudioTrack object.