ifdtool: Enable warnings as errors, and fix any issues

Change-Id: Id462a10c2affac54ec48a1cc2a5b2ca66112848e
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/11613
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

util/ifdtool/Makefile

@@ -22,7 +22,7 @@ PROGRAM = ifdtool
 CC      = gcc
 INSTALL = /usr/bin/install
 PREFIX  = /usr/local
-CFLAGS  = -O2 -g -Wall -W
+CFLAGS  = -O2 -g -Wall -W -Werror
 LDFLAGS =
 
 OBJS = ifdtool.o