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

Test: builds OK
Change-Id: I87975a8367bd6dfdf73449ae66e2b6e9271772b2
diff --git a/src/android/channels.cpp b/src/android/channels.cpp
index 4f3e976..6f0434f 100644
--- a/src/android/channels.cpp
+++ b/src/android/channels.cpp
@@ -15,6 +15,7 @@
  */
 
 #include "sles_allinclusive.h"
+#include <cutils/bitops.h>
 #include <system/audio.h>
 #include <SLES/OpenSLES_Android.h>
 #include "channels.h"