LinuxKPI: return value for linux_pci_probe()

In linux_pci_probe() return BUS_PROBE_DEFAULT rather than 0
(which actually is BUS_PROBE_SPECIFIC and means 'Only this
driver can use this device').

Sponsored by: The FreeBSD Foundation
Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D33913

(cherry picked from commit 39d8c3870752c597700c32c9dd57d421a1334611)