util/*/Makefile: Rename -W to -Wextra

-W is the old name for -Wextra, so let's rename it to be consistent with
the rest of the utility Makefiles.

Change-Id: I0e50f13d2617b785d343707fc895516574164562
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34455
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

util/nvramtool/Makefile

@@ -19,7 +19,7 @@ PROGRAM = nvramtool
 CC      = gcc
 INSTALL = /usr/bin/env install
 PREFIX  = /usr/local
-CFLAGS  = -O2 -g -Wall -W -Wmissing-prototypes -I. -DCMOS_HAL=1
+CFLAGS  = -O2 -g -Wall -Wextra -Wmissing-prototypes -I. -DCMOS_HAL=1
 #CFLAGS  = -Os -Wall
 
 CLI_OBJS = cli/nvramtool.o cli/opts.o