Use audio_session_t consistently

Bug: 27562099
Change-Id: I328d8226191386b163f2ace41233607294c50dcd
diff --git a/include/media/Visualizer.h b/include/media/Visualizer.h
index 186e018..ec0dad5 100644
--- a/include/media/Visualizer.h
+++ b/include/media/Visualizer.h
@@ -69,7 +69,7 @@
                                    int32_t priority = 0,
                                    effect_callback_t cbf = NULL,
                                    void* user = NULL,
-                                   int sessionId = 0);
+                                   audio_session_t sessionId = AUDIO_SESSION_OUTPUT_MIX);
 
                         ~Visualizer();