Fix unused parameter warnings in audio

Change-Id: I665ba3358dd9502f0adec70d486e7bf8a2e1b0fe
diff --git a/media/libmedia/AudioSystem.cpp b/media/libmedia/AudioSystem.cpp
index dcb72f8..1ab94fa 100644
--- a/media/libmedia/AudioSystem.cpp
+++ b/media/libmedia/AudioSystem.cpp
@@ -333,7 +333,7 @@
 }
 
 status_t AudioSystem::getLatency(audio_io_handle_t output,
-                                 audio_stream_type_t streamType,
+                                 audio_stream_type_t streamType __unused,
                                  uint32_t* latency)
 {
     OutputDescriptor *outputDesc;