Use audio_stream_type_t consistently

Change-Id: I1e92f018a07e4b1b73ef8d4de461ef1e08bc48e7
diff --git a/include/hardware/audio_policy.h b/include/hardware/audio_policy.h
index fc56e5e..add14f8 100644
--- a/include/hardware/audio_policy.h
+++ b/include/hardware/audio_policy.h
@@ -215,7 +215,7 @@
     int (*set_effect_enabled)(struct audio_policy *pol, int id, bool enabled);
 
     bool (*is_stream_active)(const struct audio_policy *pol,
-                             int stream,
+                             audio_stream_type_t stream,
                              uint32_t in_past_ms);
 
     /* dump state */