MP2: replace AudioSystem APIs with public ones in mediaplayer2.cpp

Bug: 112549970
Test: MediaPlayer2Test, RoutingTest

Change-Id: Ib2520c29370dee88667e64044b3fcdc053623dbf
diff --git a/media/libmediaplayer2/include/mediaplayer2/MediaPlayer2Interface.h b/media/libmediaplayer2/include/mediaplayer2/MediaPlayer2Interface.h
index 07a7946..4b19e38 100644
--- a/media/libmediaplayer2/include/mediaplayer2/MediaPlayer2Interface.h
+++ b/media/libmediaplayer2/include/mediaplayer2/MediaPlayer2Interface.h
@@ -94,7 +94,7 @@
         virtual status_t getTimestamp(AudioTimestamp &ts) const = 0;
         virtual int64_t getPlayedOutDurationUs(int64_t nowUs) const = 0;
         virtual status_t getFramesWritten(uint32_t *frameswritten) const = 0;
-        virtual audio_session_t getSessionId() const = 0;
+        virtual int32_t getSessionId() const = 0;
         virtual audio_stream_type_t getAudioStreamType() const = 0;
         virtual uint32_t getSampleRate() const = 0;
         virtual int64_t getBufferDurationInUs() const = 0;