PCI: Use request_resource_conflict() instead of insert_ for bus numbers

If a conflict happens during insert_resource_conflict() and all conflicts
fit within the newly inserted resource then they will become children of
the new resource. This is almost certainly not what we want for bus
numbers.

Signed-off-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>