Move buffers pointer out of the control block

This is part of a series to clean up the control block.

Change-Id: Ie474557db7cb360f2d9a0f11600a68f5a3d46f07
diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index 6e88032..639b567 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -510,6 +510,7 @@
     uint32_t                mFrameCount;
 
     audio_track_cblk_t*     mCblk;                  // re-load after mLock.unlock()
+    void*                   mBuffers;               // starting address of buffers in shared memory
     audio_format_t          mFormat;
     audio_stream_type_t     mStreamType;
     uint8_t                 mChannelCount;