PCI: allow pci_alloc_child_bus() to handle a NULL bridge

Allow pci_alloc_child_bus() to allocate buses without bridge devices.
Some SR-IOV devices can occupy more than one bus number, but there is no
explicit bridges because that have internal routing mechanism.

Signed-off-by: Yu Zhao <[e-mail]>
Signed-off-by: Jesse Barnes <[e-mail]>

drivers/pci/probe.c

···
 	if (!child)
 		return NULL;
 
-	child->self = bridge;
 	child->parent = parent;
 	child->ops = parent->ops;
 	child->sysdata = parent->sysdata;
 	child->bus_flags = parent->bus_flags;
-	child->bridge = get_device(&bridge->dev);
 
 	/* initialize some portions of the bus device, but don't register it
 	 * now as the parent is not properly set up yet.  This device will get
···
 	child->number = child->secondary = busnr;
 	child->primary = parent->secondary;
 	child->subordinate = 0xff;
+
+	if (!bridge)
+		return child;
+
+	child->self = bridge;
+	child->bridge = get_device(&bridge->dev);
 
 	/* Set up default resource pointers and names.. */
 	for (i = 0; i < PCI_BRIDGE_RESOURCE_NUM; i++) {