USB: serial: io_ti: fix I/O after disconnect

Cancel the heartbeat work on driver unbind in order to avoid I/O after
disconnect in case the port is held open.

Note that the cancel in release() is still needed to stop the heartbeat
after late probe errors.

Fixes: 26c78daa ("USB: io_ti: Add heartbeat to keep idle EP/416
ports from disconnecting")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/io_ti.c

@@ -2590,6 +2590,9 @@ static int edge_startup(struct usb_serial *serial)
 
 static void edge_disconnect(struct usb_serial *serial)
 {
+	struct edgeport_serial *edge_serial = usb_get_serial_data(serial);
+
+	cancel_delayed_work_sync(&edge_serial->heartbeat_work);
 }
 
 static void edge_release(struct usb_serial *serial)