vboot: fix up load_kernel_test to store subkey in workbuf
vboot: fix up load_kernel_test to store subkey in workbuf

Since CL:1651221, kernel subkey has been stored and accessed
as part of vboot2 workbuf.  We forgot to update the utility
load_kernel_test to follow suit.

BUG=b:124141368, chromium:1038260
TEST=make clean && make runtests
BRANCH=none

Change-Id: I67686dc9dd555d3cce9d1be287b56c108460239b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2054268
Commit-Queue: Joel Kitching <c2feea8c1334a0d339e816ae4c7c9ecfa9b30a91@chromium.org>
Tested-by: Joel Kitching <c2feea8c1334a0d339e816ae4c7c9ecfa9b30a91@chromium.org>
Reviewed-by: Julius Werner <4d12f06cff3725783b352157673a720bc67c4afe@chromium.org>

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