PCI: Don't try to disable Bus Master on disconnected PCI devices

This is a fix for commit 7897e60 ("PCI: Disable Bus Master
unconditionally in pci_device_shutdown()").  Vivek reported that
with this commit, kexec failed because none of his SATA disks
came up.

A ->shutdown() callback might put the device in D3cold, which means config
space is no longer available.

[bhelgaas: changelog]
Link: https://lkml.org/lkml/2013/3/12/529
Reported-and-Tested-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/pci/pci-driver.c

@@ -390,9 +390,10 @@ static void pci_device_shutdown(struct device *dev)
 
 	/*
 	 * Turn off Bus Master bit on the device to tell it to not
-	 * continue to do DMA
+	 * continue to do DMA. Don't touch devices in D3cold or unknown states.
 	 */
-	pci_clear_master(pci_dev);
+	if (pci_dev->current_state <= PCI_D3hot)
+		pci_clear_master(pci_dev);
 }
 
 #ifdef CONFIG_PM