Rename control block server to mServer and add comments

Change-Id: Ieabd91acee92d0e84e66fbd358df5282b856306e
diff --git a/services/audioflinger/Tracks.cpp b/services/audioflinger/Tracks.cpp
index 3e184b4..4f2e372 100644
--- a/services/audioflinger/Tracks.cpp
+++ b/services/audioflinger/Tracks.cpp
@@ -468,7 +468,7 @@
             mAudioTrackServerProxy->getSampleRate(),
             20.0 * log10((vlr & 0xFFFF) / 4096.0),
             20.0 * log10((vlr >> 16) / 4096.0),
-            mCblk->server,
+            mCblk->mServer,
             (int)mMainBuffer,
             (int)mAuxBuffer,
             mCblk->flags,
@@ -1739,7 +1739,7 @@
             mChannelMask,
             mSessionId,
             mState,
-            mCblk->server,
+            mCblk->mServer,
             mFrameCount);
 }