pci_host_generic: Set a valid error if allocating a range resource fails

Previously pci_host_generic_attach was returning 0 (success)
incorrectly if allocating a range failed. The error value was 0 from
the previously successful call to bus_set_resource in this case.

Fixes: d79b6b8ec267 pci_host_generic: Don't rewrite resource start address for translation