PCI: add default busn_resource

We need to put into the resources list for legacy system.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
diff --git a/include/linux/pci.h b/include/linux/pci.h
index c4df570..8c8b44d 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -368,6 +368,8 @@
 	return (pdev->error_state != pci_channel_io_normal);
 }
 
+extern struct resource busn_resource;
+
 struct pci_host_bridge_window {
 	struct list_head list;
 	struct resource *res;		/* host bridge aperture (CPU address) */