fix up some implicit declarations

Change-Id: Ia98bb5bea04a9cb87bf1993687e7f91f46022509
diff --git a/flashutils/flashutils.c b/flashutils/flashutils.c
index 7dc750c..2f8da41 100644
--- a/flashutils/flashutils.c
+++ b/flashutils/flashutils.c
@@ -2,6 +2,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <sys/wait.h>
+#include <stdio.h>
 
 #include "flashutils/flashutils.h"