Fix clang warnings in AudioFlinger

Change-Id: I0fa61025c979709ad7d655bc717df5f194b6089e
diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index e0d1404..0137c66 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -60,8 +60,8 @@
 
 namespace android {
 
-class audio_track_cblk_t;
-class effect_param_cblk_t;
+struct audio_track_cblk_t;
+struct effect_param_cblk_t;
 class AudioMixer;
 class AudioBuffer;
 class AudioResampler;