Include what you use

Change-Id: I1967861f383bb5ed6743fb69e3bd439907ed7033
diff --git a/services/audioflinger/FastMixer.cpp b/services/audioflinger/FastMixer.cpp
index 8f05ef0..67e2e6e 100644
--- a/services/audioflinger/FastMixer.cpp
+++ b/services/audioflinger/FastMixer.cpp
@@ -27,6 +27,7 @@
 
 #include "Configuration.h"
 #include <time.h>
+#include <utils/Debug.h>
 #include <utils/Log.h>
 #include <utils/Trace.h>
 #include <system/audio.h>