Fix code warning.

Change-Id: Ib11fb49f528d3688351ae349d5b4e307c28b3967
diff --git a/mbtk/mbtk_utils/device_info.c b/mbtk/mbtk_utils/device_info.c
index 6d22c34..864cb36 100755
--- a/mbtk/mbtk_utils/device_info.c
+++ b/mbtk/mbtk_utils/device_info.c
@@ -1,3 +1,4 @@
+#include <string.h>
 #include "mbtk_type.h"
 #include "mbtk_device.h"