ipack: ipoctal: fix tty registration race

Make sure to set the tty class-device driver data before registering the
tty to avoid having a racing open() dereference a NULL pointer.

Fixes: 9c1d784afc6f ("Staging: ipack/devices/ipoctal: Get rid of ipoctal_list.")
Cc: [e-mail] # 3.7
Acked-by: Samuel Iglesias Gonsalvez <[e-mail]>
Signed-off-by: Johan Hovold <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/ipack/devices/ipoctal.c

···
 		spin_lock_init(&channel->lock);
 		channel->pointer_read = 0;
 		channel->pointer_write = 0;
-		tty_dev = tty_port_register_device(&channel->tty_port, tty, i, NULL);
+		tty_dev = tty_port_register_device_attr(&channel->tty_port, tty,
+							i, NULL, channel, NULL);
 		if (IS_ERR(tty_dev)) {
 			dev_err(&ipoctal->dev->dev, "Failed to register tty device.\n");
 			tty_port_destroy(&channel->tty_port);
 			continue;
 		}
-		dev_set_drvdata(tty_dev, channel);
 	}
 
 	/*