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/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index 1417105..fc24bed 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -1035,6 +1035,7 @@
             AudioBufferProvider::Buffer mOutBuffer;
             bool                        mActive;
             DuplicatingThread* const mSourceThread; // for waitTimeMs() in write()
+            void*                       mBuffers;   // starting address of buffers in plain memory
         };  // end of OutputTrack
 
         PlaybackThread(const sp<AudioFlinger>& audioFlinger, AudioStreamOut* output,