wifi: iwlwifi: pcie: rescan bus if no parent

If the bus has no parent due to the topology, the device rescan
(after some kind of reset was detected) wouldn't work. On the
other hand, some platforms appear to require scanning the parent,
though it's not clear why.

However if there's no parent, then we skip the rescan, which isn't a
good idea. Change the code to go to the parent only if that exists,
and rescan the bus itself where it doesn't.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230913145231.f7795a1ccdab.I2b84810a743469a1bcabf3628262cf54311593f4@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/intel/iwlwifi/pcie/trans.c

@@ -2112,8 +2112,11 @@ static void iwl_trans_pcie_removal_wk(struct work_struct *wk)
 	pci_lock_rescan_remove();
 	pci_dev_put(pdev);
 	pci_stop_and_remove_bus_device(pdev);
-	if (removal->rescan)
-		pci_rescan_bus(bus->parent);
+	if (removal->rescan && bus) {
+		if (bus->parent)
+			bus = bus->parent;
+		pci_rescan_bus(bus);
+	}
 	pci_unlock_rescan_remove();
 
 	kfree(removal);