USB: serial: refactor generic close

Export usb_serial_generic_close so that drivers can easily kill the read
and write urb and make sure that the write fifo is reset.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/serial/mct_u232.c b/drivers/usb/serial/mct_u232.c
index 2849f8c..7aa01b9 100644
--- a/drivers/usb/serial/mct_u232.c
+++ b/drivers/usb/serial/mct_u232.c
@@ -549,12 +549,9 @@
 {
 	dbg("%s port %d", __func__, port->number);
 
-	if (port->serial->dev) {
-		/* shutdown our urbs */
-		usb_kill_urb(port->write_urb);
-		usb_kill_urb(port->read_urb);
+	usb_serial_generic_close(port);
+	if (port->serial->dev)
 		usb_kill_urb(port->interrupt_in_urb);
-	}
 } /* mct_u232_close */