util/inteltool: Add missing #include <string.h>

Change-Id: I7bb142d9f936b73e84d301028069d85cc15d596a
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/25143
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

util/inteltool/inteltool.c

@@ -18,6 +18,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <inttypes.h>
 #include <getopt.h>
 #include <fcntl.h>