PCI: Allow release of resources that were never assigned

It is entirely possible that the BIOS wasn't able to assign resources to a
device. In this case don't crash in pci_release_resource() when we try to
resize the resource.

Fixes: 8bb705e3

 ("PCI: Add pci_resize_resource() for resizing BARs")
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
CC: stable@vger.kernel.org	# v4.15+