Revert "staging: comedi: drivers: Remove unneeded NULL check before kfree()"

This reverts commit 3545bee9.

It's not correct.
Reported-by: Hartley Sweeten <HartleyS@visionengravers.com>
Cc: Janani Ravichandran <janani.rvchndrn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/amplc_pci224.c

@@ -1096,8 +1096,10 @@ static void pci224_detach(struct comedi_device *dev)
 	struct pci224_private *devpriv = dev->private;
 
 	comedi_pci_detach(dev);
-	kfree(devpriv->ao_scan_vals);
-	kfree(devpriv->ao_scan_order);
+	if (devpriv) {
+		kfree(devpriv->ao_scan_vals);
+		kfree(devpriv->ao_scan_order);
+	}
 }
 
 static struct comedi_driver amplc_pci224_driver = {