dummyflasher: Replace another case of `sizeof(struct ...)`

Using the pointer's type instead ensures that we get the right size even
if code changes in the future.

Change-Id: If88ba394095f86c598dcc5cf1751e1c23b132d04
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/55358
Original-Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Original-Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72208
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
1 file changed