[ACPI] fix run-time error checking in acpi_pci_irq_disable()

The 'bus' field in pci_dev structure should be checked before calling
pci_read_config_byte() because pci_bus_read_config_byte() called by
pci_read_config_byte() refers to 'bus' field.
Signed-off-by: NKenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLen Brown <len.brown@intel.com>

drivers/acpi/pci_irq.c

@@ -500,7 +500,7 @@ void acpi_pci_irq_disable(struct pci_dev *dev)
 
 	ACPI_FUNCTION_TRACE("acpi_pci_irq_disable");
 
-	if (!dev)
+	if (!dev || !dev->bus)
 		return_VOID;
 
 	pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin);
@@ -508,9 +508,6 @@ void acpi_pci_irq_disable(struct pci_dev *dev)
 		return_VOID;
 	pin--;
 
-	if (!dev->bus)
-		return_VOID;
-
 	/*
 	 * First we check the PCI IRQ routing table (PRT) for an IRQ.
 	 */