nvramtool: write size field more obviously

The field wasn't initialized in RAM first and later overwritten in a somewhat
twisted way (that relied on the size field coming after the tag field in the
struct).

Change-Id: Ibe931b297df51e3c46ae163e059338781f5a27e2
Found-by: Coverity Scan
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/4087
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)
1 file changed