Revert "image-fit: switch ENOLINK to ENOENT"

As while I want to support OpenBSD hosts, this change broke FIT images
as in the image checking code we care about ENOLINK and on further
review we need to think about what to change ENOLINK to so we can be
sure to handle the different cases here.

This reverts commit bac17b78.

Signed-off-by: Tom Rini <trini@konsulko.com>