PCI: Check device_attach() return value always

Previously we checked the device_attach() return value only when
CONFIG_BUG=y.  That caused this warning in builds where CONFIG_BUG is not
set:

  drivers/pci/bus.c:237:6: warning: variable 'retval' set but not used [-Wunused-but-set-variable]

Check the return value of device_attach() always and clean up after
failure.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/pci/bus.c

@@ -291,7 +291,12 @@ void pci_bus_add_device(struct pci_dev *dev)
 
 	dev->match_driver = true;
 	retval = device_attach(&dev->dev);
-	WARN_ON(retval < 0);
+	if (retval < 0) {
+		dev_warn(&dev->dev, "device attach failed (%d)\n", retval);
+		pci_proc_detach_device(dev);
+		pci_remove_sysfs_dev_files(dev);
+		return;
+	}
 
 	dev->is_added = 1;
 }