PCI: shpchp: Check bridge's secondary (not primary) bus speed

When a new device is added below a hotplug bridge, the bridge's secondary
bus speed and the device's bus speed must match.  The shpchp driver
previously checked the bridge's *primary* bus speed, not the secondary bus
speed.

This caused hot-add errors like:

  shpchp 0000:00:03.0: Speed of bus ff and adapter 0 mismatch

Check the secondary bus speed instead.

[bhelgaas: changelog]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=75251
Fixes: 3749c51a ("PCI: Make current and maximum bus speeds part of the PCI core")
Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
CC: stable@vger.kernel.org	# v2.6.34+

drivers/pci/hotplug/shpchp_ctrl.c

@@ -282,8 +282,8 @@ static int board_added(struct slot *p_slot)
 		return WRONG_BUS_FREQUENCY;
 	}
 
-	bsp = ctrl->pci_dev->bus->cur_bus_speed;
-	msp = ctrl->pci_dev->bus->max_bus_speed;
+	bsp = ctrl->pci_dev->subordinate->cur_bus_speed;
+	msp = ctrl->pci_dev->subordinate->max_bus_speed;
 
 	/* Check if there are other slots or devices on the same bus */
 	if (!list_empty(&ctrl->pci_dev->subordinate->devices))