As we want to allocate an array of `flashrom_board_info` structs, use
that type in sizeof. This did not cause problems as `board_info` was at
least as big as `flashrom_board_info`, but nothing guarantees it.

Change-Id: I66e875d54c9a7cc59898b072b052282b0b5cbb2f
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/39973


Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Michael Niewöhner
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>