PCI: Use res->parent to check if resource is assigned

reassign_resources_sorted() uses resource_size() to select between
pci_assign_resource() and pci_reassign_resource(). Due to twisted way
bridge window sizing in pbus_size_mem() sets resource sizes to 0, it works
to match into IOV resources but that is going to be changed by an upcoming
change.

Replace resource_size() check with res->parent check that is the true
dividing line in between whether assign or reassign function should be used
for the resource.

Link: https://lore.kernel.org/r/20241216175632.4175-24-ilpo.jarvinen@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Xiaochun Lee <lixc17@lenovo.com>

drivers/pci/setup-bus.c

@@ -271,7 +271,7 @@ static void reassign_resources_sorted(struct list_head *realloc_head,
 		res_name = pci_resource_name(dev, idx);
 		add_size = add_res->add_size;
 		align = add_res->min_align;
-		if (!resource_size(res)) {
+		if (!res->parent) {
 			resource_set_range(res, align, add_size);
 			if (pci_assign_resource(dev, idx)) {
 				pci_dbg(dev,