wingray/audio: fix build

Change-Id: Id153ec554a2d1ce9a02931080ab5f9356766537b
Signed-off-by: Dima Zavin <dima@android.com>
diff --git a/libaudio/AudioHardware.h b/libaudio/AudioHardware.h
index 76ea2f7..ba5a5fe 100644
--- a/libaudio/AudioHardware.h
+++ b/libaudio/AudioHardware.h
@@ -33,6 +33,7 @@
 #endif
 
 namespace android_audio_legacy {
+    using android::AutoMutex;
     using android::Mutex;
     using android::SortedVector;