fix the ulog build error

components/utilities/ulog/ulog.c

@@ -7,7 +7,7 @@
  * Date           Author       Notes
  * 2018-08-25     armink       the first version
  */
-
+#include <stdlib.h>
 #include <stdarg.h>
 #include "ulog.h"
 #include "rthw.h"