hal: compilation fix for extended feature flags

- Fix compilation error for offload, Dolby,
  HDMI pass through, FLAC decoder, and hardware
  accelerated effects when extended feature
  flags are disabled.

Change-Id: I5b36d7668f63a396ed930d62c0337c2c3f311c95
diff --git a/hal/audio_hw.h b/hal/audio_hw.h
index 67f5279..5e61d36 100644
--- a/hal/audio_hw.h
+++ b/hal/audio_hw.h
@@ -38,6 +38,7 @@
 #ifndef QCOM_AUDIO_HW_H
 #define QCOM_AUDIO_HW_H
 
+#include <stdlib.h>
 #include <cutils/list.h>
 #include <hardware/audio.h>
 #include <tinyalsa/asoundlib.h>