x86_64: don't need set default res if only have one root bus

if there's only one root bus there's no need to split resources.

This patch fixes the issue described at:

  http://lkml.org/lkml/2008/4/10/304Reported-and-bisected-by: NRafael J. Wysocki <rjw@sisk.pl>
Tested-by: NRafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: NYinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

arch/x86/pci/k8-bus_64.c

@@ -69,7 +69,8 @@ void set_pci_bus_resources_arch_default(struct pci_bus *b)
 	int j;
 	struct pci_root_info *info;
 
-	if (!pci_root_num)
+	/* if only one root bus, don't need to anything */
+	if (pci_root_num < 2)
 		return;
 
 	for (i = 0; i < pci_root_num; i++) {