staging: comedi: kcomedilib_main: (!foo) preferred over (foo == NULL)

Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: NIan Abbott <abbotti@mev.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/kcomedilib/kcomedilib_main.c

@@ -58,7 +58,7 @@ struct comedi_device *comedi_open(const char *filename)
 		retval = NULL;
 	up_read(&dev->attach_lock);
 
-	if (retval == NULL)
+	if (!retval)
 		comedi_dev_put(dev);
 
 	return retval;