USB: serial: remove redundant write-urb kill

Since commit 1ce7b934 ("USB: serial: reuse generic write urb and
bulk-out buffer") the port write_urb is simply a pointer to the first
member of write_urbs so there's no need to kill it twice.
Signed-off-by: NJohan Hovold <jhovold@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/generic.c

@@ -144,7 +144,6 @@ static void generic_cleanup(struct usb_serial_port *port)
 	if (serial->dev) {
 		/* shutdown any bulk transfers that might be going on */
 		if (port->bulk_out_size) {
-			usb_kill_urb(port->write_urb);
 			for (i = 0; i < ARRAY_SIZE(port->write_urbs); ++i)
 				usb_kill_urb(port->write_urbs[i]);