Include what you use: <cutils/bitops.h> for popcount

Test: builds OK
Change-Id: I4ebd459a124b6480bb0ce1ccb49b76c727ced0bd
diff --git a/media/jni/audioeffect/Visualizer.cpp b/media/jni/audioeffect/Visualizer.cpp
index efeb335..f4d65d0 100644
--- a/media/jni/audioeffect/Visualizer.cpp
+++ b/media/jni/audioeffect/Visualizer.cpp
@@ -25,6 +25,7 @@
 #include <limits.h>
 
 #include <audio_utils/fixedfft.h>
+#include <cutils/bitops.h>
 #include <utils/Thread.h>
 
 #include "Visualizer.h"