sandbox: Fix set_working_fdt_addr users

When running sandbox with the new pointer sanitization we just recently
introduced, we're running into a case with FIT images where we end up
interpreting pointers as addresses.

What happened is that most callers of set_working_fdt_addr() simply
convert pointers into addresses without taking into account that they
might be 2 separate address spaces. Fix the callers up to map their
pointers into addresses.

This makes sandbox tests pass for me again.

Signed-off-by: Alexander Graf <agraf@suse.de>