memory_bus: Drop stale `size == 0` workaround and FIXME

All chips using the prepare_memory_mapping() function have a size set.

Change-Id: Id5c56a1ebd00563de162b74f762c23aaa0e6d824
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/72524
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
1 file changed