powerpc/pseries: extract host bridge from pci_bus prior to bus removal

The pci_bus->bridge reference may no longer be valid after
pci_bus_remove() resulting in passing a bad value to device_unregister()
for the associated bridge device.

Store the host_bridge reference in a separate variable prior to
pci_bus_remove().

Fixes: 73400565 ("powerpc/pci: Reorder pci bus/bridge unregistration during PHB removal")
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210211182435.47968-1-tyreld@linux.ibm.com

arch/powerpc/platforms/pseries/pci_dlpar.c

@@ -50,6 +50,7 @@ EXPORT_SYMBOL_GPL(init_phb_dynamic);
 int remove_phb_dynamic(struct pci_controller *phb)
 {
 	struct pci_bus *b = phb->bus;
+	struct pci_host_bridge *host_bridge = to_pci_host_bridge(b->bridge);
 	struct resource *res;
 	int rc, i;
 
@@ -76,7 +77,8 @@ int remove_phb_dynamic(struct pci_controller *phb)
 	/* Remove the PCI bus and unregister the bridge device from sysfs */
 	phb->bus = NULL;
 	pci_remove_bus(b);
-	device_unregister(b->bridge);
+	host_bridge->bus = NULL;
+	device_unregister(&host_bridge->dev);
 
 	/* Now release the IO resource */
 	if (res->flags & IORESOURCE_IO)