Fix code warning.

Change-Id: Ib11fb49f528d3688351ae349d5b4e307c28b3967
diff --git a/mbtk/libmbtk_lib/common/mbtk_adc.c b/mbtk/libmbtk_lib/common/mbtk_adc.c
index 55cce7c..601d9b0 100755
--- a/mbtk/libmbtk_lib/common/mbtk_adc.c
+++ b/mbtk/libmbtk_lib/common/mbtk_adc.c
@@ -16,6 +16,9 @@
 #include <sys/stat.h>
 #include <sys/statfs.h>
 #include <sys/types.h>
+#include <unistd.h>
+#include <stdlib.h>
+
 #include "mbtk_log.h"
 #include "mbtk_type.h"
 #include "mbtk_adc.h"