Fix verification with sparse layouts

The full verification step was not accounting for sparse layouts.
Instead of the old contents, combine_image_by_layout() implicitly
assumed the new contents for unspecified regions.

Change-Id: I44e0cea621f2a3d4dc70fa7e93c52ed95e54014a
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/30370
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
3 files changed