powerpc/pci: Fix checking for child bridges in PCI code.

pci_device_to_OF_node() can return null, and list_for_each_entry will
never enter the loop when dev is NULL, so it looks like this test is
a typo.
Reported-by: NJulia Lawall <julia@diku.dk>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/pci_of_scan.c

@@ -336,7 +336,8 @@ static void __devinit __of_scan_bus(struct device_node *node,
 		if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE ||
 		    dev->hdr_type == PCI_HEADER_TYPE_CARDBUS) {
 			struct device_node *child = pci_device_to_OF_node(dev);
-			of_scan_pci_bridge(child, dev);
+			if (child)
+				of_scan_pci_bridge(child, dev);
 		}
 	}
 }