iwlwifi: adjust the LinuxKPI pci return for now

Rather than having LinuxKPI return BUS_PROBE_DEFAULT, return
"one less" so that on conflict of IDs others would be preferred.

This means that iwm(4) will attach instead of iwlwifi(4) for the
chipsets iwm(4) supports and iwlwifi(4) only for the other--in iwm(4)
unsupported--chipsets. This is done so that we can enable auto-loading
of drivers but for the upcoming 13.1-Release people with working iwm(4)
will not yet be affected by iwlwifi(4).

Sponsored by: The FreeBSD Foundation
MFC after: 3 days