Fix clang warnings in AudioFlinger

Change-Id: I0fa61025c979709ad7d655bc717df5f194b6089e
diff --git a/include/media/AudioEffect.h b/include/media/AudioEffect.h
index 05d834d..f3024b7 100644
--- a/include/media/AudioEffect.h
+++ b/include/media/AudioEffect.h
@@ -36,7 +36,7 @@
 
 // ----------------------------------------------------------------------------
 
-class effect_param_cblk_t;
+struct effect_param_cblk_t;
 
 // ----------------------------------------------------------------------------