PCI: Use device_release_driver() in pci_stop_root_bus()

To be consistent with 4bff6749

 ("PCI: Move device_del() from
pci_stop_dev() to pci_destroy_dev()", this changes pci_stop_root_bus()
to use device_release_driver() instead of device_del().

This also changes pci_remove_root_bus() to use device_unregister()
instead of put_device() so it corresponds with the device_register()
call in pci_create_root_bus().

[bhelgaas: changelog]
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>