Add missing includes.

Change-Id: I91730363386dae6ecb2193ec8f50ba9f8fc0ad60
diff --git a/modules/audio/audio_hw.c b/modules/audio/audio_hw.c
index 18c0e59..637e3f4 100644
--- a/modules/audio/audio_hw.c
+++ b/modules/audio/audio_hw.c
@@ -18,6 +18,7 @@
 //#define LOG_NDEBUG 0
 
 #include <errno.h>
+#include <malloc.h>
 #include <pthread.h>
 #include <stdint.h>
 #include <sys/time.h>