USB: symbolserial: Use usb_get_serial_port_data

The driver used usb_get_serial_data(port->serial) which compiled but resulted
in a NULL pointer being returned (and subsequently used). I did not go deeper
into this but I guess this is a regression.
Signed-off-by: Philipp Hachtmann <hachti@hachti.de>
Fixes: a85796ee ("USB: symbolserial: move private-data allocation to
port_probe")
Cc: stable <stable@vger.kernel.org>     # v3.10
Acked-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/symbolserial.c

@@ -94,7 +94,7 @@ static void symbol_int_callback(struct urb *urb)
 
 static int symbol_open(struct tty_struct *tty, struct usb_serial_port *port)
 {
-	struct symbol_private *priv = usb_get_serial_data(port->serial);
+	struct symbol_private *priv = usb_get_serial_port_data(port);
 	unsigned long flags;
 	int result = 0;
 
@@ -120,7 +120,7 @@ static void symbol_close(struct usb_serial_port *port)
 static void symbol_throttle(struct tty_struct *tty)
 {
 	struct usb_serial_port *port = tty->driver_data;
-	struct symbol_private *priv = usb_get_serial_data(port->serial);
+	struct symbol_private *priv = usb_get_serial_port_data(port);
 
 	spin_lock_irq(&priv->lock);
 	priv->throttled = true;
@@ -130,7 +130,7 @@ static void symbol_throttle(struct tty_struct *tty)
 static void symbol_unthrottle(struct tty_struct *tty)
 {
 	struct usb_serial_port *port = tty->driver_data;
-	struct symbol_private *priv = usb_get_serial_data(port->serial);
+	struct symbol_private *priv = usb_get_serial_port_data(port);
 	int result;
 	bool was_throttled;