AudioFlinger: rename variables to clarify reference to track channel count or channel mask

Some variables and structure members should be renamed to reflect the fact that they contain the
number of channels in a track (channel count) or the actual channels used by a track (channel mask).
Especially member "channels" of track control block (struct audio_track_cblk_t) is actually the
number of channels (channels count).

Change-Id: I220c8dede9fc00c8a5693389e790073b6ed307b8
diff --git a/include/private/media/AudioTrackShared.h b/include/private/media/AudioTrackShared.h
index 8e2db20..ab5ac64 100644
--- a/include/private/media/AudioTrackShared.h
+++ b/include/private/media/AudioTrackShared.h
@@ -59,7 +59,7 @@
                 // 8 bit PCM data: in this case,  mCblk->frameSize is based on a sample size of
                 // 16 bit because data is converted to 16 bit before being stored in buffer
                 uint32_t    frameSize;
-                uint8_t     channels;
+                uint8_t     channelCount;
                 uint8_t     flowControlFlag; // underrun (out) or overrrun (in) indication
                 uint8_t     out;        // out equals 1 for AudioTrack and 0 for AudioRecord
                 uint8_t     forceReady;