x86/PCI: Remove unused pci_root_bus

pci_root_bus is unused, so remove all references to it.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
diff --git a/arch/x86/pci/legacy.c b/arch/x86/pci/legacy.c
index a1df191..a9e8308 100644
--- a/arch/x86/pci/legacy.c
+++ b/arch/x86/pci/legacy.c
@@ -30,7 +30,7 @@
 	}
 
 	printk("PCI: Probing PCI hardware\n");
-	pci_root_bus = pcibios_scan_root(0);
+	pcibios_scan_root(0);
 	return 0;
 }