Update AudioTrack comments to match AudioRecord

Change-Id: I176a4830513a0b37c38f86815fe637093b9ad52f
diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index 0094ff0..e919dd4 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -91,7 +91,7 @@
             void*       raw;
             short*      i16;      // signed 16-bit
             int8_t*     i8;       // unsigned 8-bit, offset by 0x80
-        };                        // input: unused, output: pointer to buffer
+        };                        // input to obtainBuffer(): unused, output: pointer to buffer
     };
 
     /* As a convenience, if a callback is supplied, a handler thread