PCI: Add device even if driver attach failed

device_attach() returning failure indicates a driver error while trying to
probe the device. In such a scenario, the PCI device should still be added
in the system and be visible to the user.

When device_attach() fails, merely warn about it and keep the PCI device in
the system.

This partially reverts ab1a187bba5c ("PCI: Check device_attach() return
value always").

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rajat Jain <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Cc: [e-mail] # v4.6+

drivers/pci/bus.c

···
 
 	dev->match_driver = true;
 	retval = device_attach(&dev->dev);
-	if (retval < 0 && retval != -EPROBE_DEFER) {
+	if (retval < 0 && retval != -EPROBE_DEFER)
 		pci_warn(dev, "device attach failed (%d)\n", retval);
-		pci_proc_detach_device(dev);
-		pci_remove_sysfs_dev_files(dev);
-		return;
-	}
 
 	pci_dev_assign_added(dev, true);
 }