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: If64d5fa5d124b42d40d7e123b887db8e0a5d7426
diff --git a/hal/voice.c b/hal/voice.c
index 9fc1081..c00df1a 100644
--- a/hal/voice.c
+++ b/hal/voice.c
@@ -22,6 +22,7 @@
 #define LOG_NDDEBUG 0
 
 #include <errno.h>
+#include <stdlib.h>
 #include <math.h>
 #include <cutils/log.h>
 #include <cutils/str_parms.h>