Use audio_mode_t consistently

It was int or uint32_t.
Also make getMode() const.

Change-Id: Ibe45aadbf413b9158e4dd17f2b3bcc6355288d37
diff --git a/include/media/IAudioFlinger.h b/include/media/IAudioFlinger.h
index 9e3cb7f..b4a1970 100644
--- a/include/media/IAudioFlinger.h
+++ b/include/media/IAudioFlinger.h
@@ -96,7 +96,7 @@
     virtual     bool        streamMute(int stream) const = 0;
 
     // set audio mode
-    virtual     status_t    setMode(int mode) = 0;
+    virtual     status_t    setMode(audio_mode_t mode) = 0;
 
     // mic mute/state
     virtual     status_t    setMicMute(bool state) = 0;