s390/smsgiucv: disable SMSG on module unload

The module exit function of the smsgiucv module uses the incorrect CP
command to disable SMSG messages. The correct command is "SET SMSG OFF".
Use it.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/net/smsgiucv.c

@@ -176,7 +176,7 @@ static struct device_driver smsg_driver = {
 
 static void __exit smsg_exit(void)
 {
-	cpcmd("SET SMSG IUCV", NULL, 0, NULL);
+	cpcmd("SET SMSG OFF", NULL, 0, NULL);
 	device_unregister(smsg_dev);
 	iucv_unregister(&smsg_handler, 1);
 	driver_unregister(&smsg_driver);