Rename mixBuffer to mMixerBuffer in FastMixer

Likewise mixBufferState becomes mMixerBufferState.
This harmonizes with the naming in AF::MixerThread.

Change-Id: I1255d7c07cc2c6ee925d7430925236d2bd163122
diff --git a/services/audioflinger/FastMixer.h b/services/audioflinger/FastMixer.h
index 981c1a7..7be004a 100644
--- a/services/audioflinger/FastMixer.h
+++ b/services/audioflinger/FastMixer.h
@@ -63,8 +63,8 @@
     NBAIO_Sink *outputSink;
     int outputSinkGen;
     AudioMixer* mixer;
-    short *mixBuffer;
-    enum {UNDEFINED, MIXED, ZEROED} mixBufferState;
+    short *mMixerBuffer;
+    enum {UNDEFINED, MIXED, ZEROED} mMixerBufferState;
     NBAIO_Format format;
     unsigned sampleRate;
     int fastTracksGen;