Treat mChannelCount as uint32_t consistently

mChannelCount was 8-, 16-, or 32-bits

Change-Id: I2cc2fedf3e33144e5c8bbd9894763282d9217f63
diff --git a/services/audioflinger/Threads.h b/services/audioflinger/Threads.h
index c5818ae..a17c279 100644
--- a/services/audioflinger/Threads.h
+++ b/services/audioflinger/Threads.h
@@ -267,7 +267,7 @@
                 size_t                  mFrameCount;       // output HAL, direct output, record
                 size_t                  mNormalFrameCount; // normal mixer and effects
                 audio_channel_mask_t    mChannelMask;
-                uint16_t                mChannelCount;
+                uint32_t                mChannelCount;
                 size_t                  mFrameSize;
                 audio_format_t          mFormat;