vboot_ref/cgpt: Consolidate flashrom write cmd paths

Small refactor to make it easier to more towards libflashrom.

BUG=b:207808292,b:220079643
BRANCH=none
TEST=`make cgpt`

Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Change-Id: Ie0c7f4faee3052300b10ba2d1adce7876d7b821c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/3469737
Tested-by: Edward O'Callaghan <quasisec@chromium.org>
Auto-Submit: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Commit-Queue: Edward O'Callaghan <quasisec@chromium.org>
1 file changed