USB: serial: ch341: handle unbound port at reset_resume

Check for NULL port data in reset_resume() to avoid dereferencing a NULL
pointer in case the port device isn't bound to a driver (e.g. after a
failed control request at port probe).

Fixes: 1ded7ea47b ("USB: ch341 serial: fix port number changed after resume")
Cc: stable <stable@vger.kernel.org>     # 2.6.30
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/ch341.c

@@ -642,9 +642,13 @@ static int ch341_tiocmget(struct tty_struct *tty)
 static int ch341_reset_resume(struct usb_serial *serial)
 {
 	struct usb_serial_port *port = serial->port[0];
-	struct ch341_private *priv = usb_get_serial_port_data(port);
+	struct ch341_private *priv;
 	int ret;
 
+	priv = usb_get_serial_port_data(port);
+	if (!priv)
+		return 0;
+
 	/* reconfigure ch341 serial port after bus-reset */
 	ch341_configure(serial->dev, priv);