audio: Remove build warnings

Change-Id: I3a31c4e9c500b60e377cd54bd2e1b400c10696f6
diff --git a/hal/audio_extn/ext_speaker.c b/hal/audio_extn/ext_speaker.c
index a551fb3..55cbb4c 100644
--- a/hal/audio_extn/ext_speaker.c
+++ b/hal/audio_extn/ext_speaker.c
@@ -18,6 +18,7 @@
 /*#define LOG_NDEBUG 0*/
 #include <cutils/log.h>
 
+#include <stdlib.h>
 #include <audio_hw.h>
 #include <dlfcn.h>
 
diff --git a/hal/voice.c b/hal/voice.c
index 044dc28..a8ccdc6 100644
--- a/hal/voice.c
+++ b/hal/voice.c
@@ -18,6 +18,7 @@
 /*#define LOG_NDEBUG 0*/
 #define LOG_NDDEBUG 0
 
+#include <stdlib.h>
 #include <errno.h>
 #include <math.h>
 #include <cutils/log.h>
diff --git a/voice_processing/voice_processing.c b/voice_processing/voice_processing.c
index 08acdb4..b3f97c6 100644
--- a/voice_processing/voice_processing.c
+++ b/voice_processing/voice_processing.c
@@ -16,6 +16,7 @@
 
 #define LOG_TAG "voice_processing"
 /*#define LOG_NDEBUG 0*/
+#include <stdlib.h>
 #include <dlfcn.h>
 #include <cutils/log.h>
 #include <cutils/list.h>