pci: allow multiple calls to pcim_enable_device()

There's no reason not to allow multiple calls to pcim_enable_device().
Calls after the first one can simply be noop. All PCI resources will
be released when the initial pcim_enable_device() resource is
released.

This allows more flexibility to managed PCI users.

Signed-off-by: Tejun Heo <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Jeff Garzik <[e-mail]>

drivers/pci/pci.c

···
 	dr = get_pci_dr(pdev);
 	if (unlikely(!dr))
 		return -ENOMEM;
-	WARN_ON(!!dr->enabled);
+	if (dr->enabled)
+		return 0;
 
 	rc = pci_enable_device(pdev);
 	if (!rc) {