PCI: Check parent for NULL in of_pci_bus_release_domain_nr()

[ Upstream commit f724590 ]

of_pci_bus_find_domain_nr() allows its parent parameter to be NULL but
of_pci_bus_release_domain_nr() (that undoes its effect) doesn't -- that
means it's going to blow up while calling of_get_pci_domain_nr() if the
parent parameter indeed happens to be NULL.  Add the missing NULL check.

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

Fixes: c14f7cc ("PCI: Assign PCI domain IDs by ida_alloc()")
Signed-off-by: Sergey Shtylyov <s.shtylyov@auroraos.dev>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260127203944.28588-1-s.shtylyov@auroraos.dev
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Sergey Shtylyov

drivers/pci/pci.c

@@ -6886,7 +6886,7 @@ static void of_pci_bus_release_domain_nr(struct device *parent, int domain_nr)
 		return;
 
 	/* Release domain from IDA where it was allocated. */
-	if (of_get_pci_domain_nr(parent->of_node) == domain_nr)
+	if (parent && of_get_pci_domain_nr(parent->of_node) == domain_nr)
 		ida_free(&pci_domain_nr_static_ida, domain_nr);
 	else
 		ida_free(&pci_domain_nr_dynamic_ida, domain_nr);