firmware: Fix more UBSAN left shift errors.
firmware: Fix more UBSAN left shift errors.

Follow up commit to CL:1867970.

Shifting a uint8_t left by 24 promotes to an int, not an unsigned int
(and shifts into the sign bit are undefined). Probably doesn't make a
difference in assembly but still doesn't hurt to fix. Courtesy of UBSAN.

BRANCH=None
BUG=chromium:1015908
TEST=No more shift errors in unit test

Change-Id: I10060df6b23da81388db34973b831c09c8d61bff
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1881475
Tested-by: Manoj Gupta <1d49d0f302d724a1dc5fc4d717d15418e9808ddd@chromium.org>
Reviewed-by: Julius Werner <4d12f06cff3725783b352157673a720bc67c4afe@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot