Staging: ipack/devices/ipoctal: fix dereference NULL pointer

After opening and closing the file /dev/ipoctal.X.Y.Z for the second time, it
gives a kernel oops due to a dereference of a NULL pointer.

The problem was that tty->driver_data was not properly initialized when
accessing the file for the second time.

Reported-by: Alberto Garcia Gonzalez <agarcia@igalia.com>
Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/ipack/devices/ipoctal.c

@@ -114,8 +114,6 @@ static int ipoctal_port_activate(struct tty_port *port, struct tty_struct *tty)
 
 	ipoctal_write_io_reg(ipoctal, &ipoctal->chan_regs[channel].u.w.cr,
 			     CR_ENABLE_RX);
-	tty->driver_data = ipoctal;
-
 	return 0;
 }
 
@@ -136,6 +134,8 @@ static int ipoctal_open(struct tty_struct *tty, struct file *file)
 	if (atomic_read(&ipoctal->open[channel]))
 		return -EBUSY;
 
+	tty->driver_data = ipoctal;
+
 	res = tty_port_open(&ipoctal->tty_port[channel], tty, file);
 	if (res)
 		return res;