Use AudioTrack::event_type not int in callback

Change-Id: Ifefc708d46874e04fd0d01cb6e2d43b987ee796c
diff --git a/include/media/ToneGenerator.h b/include/media/ToneGenerator.h
index 1ad1f26..9da069c 100644
--- a/include/media/ToneGenerator.h
+++ b/include/media/ToneGenerator.h
@@ -270,7 +270,7 @@
     unsigned int mProcessSize;  // Size of audio blocks generated at a time by audioCallback() (in PCM frames).
 
     bool initAudioTrack();
-    static void audioCallback(int event, void* user, void *info);
+    static void audioCallback(AudioTrack::event_type event, void* user, void *info);
     bool prepareWave();
     unsigned int numWaves(unsigned int segmentIdx);
     void clearWaveGens();