The one in the `dummyflasher` is a little peculiar. We actually never
knew the type of the `st_size` field in `struct stat`. It happens to
be `signed` in some systems (e.g. DJGPP).

Change-Id: If36ba22606021400b385ea6083eacc7b360c20c5
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/35800


Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>