USB: serial: fix module-license macros

Several GPL-2.0 drivers used "GPL" rather than "GPL v2" in their
MODULE_LICENSE macros; fix the macros to match the licenses.

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/serial/opticon.c b/drivers/usb/serial/opticon.c
index fd9d8aa..caa0746 100644
--- a/drivers/usb/serial/opticon.c
+++ b/drivers/usb/serial/opticon.c
@@ -417,4 +417,4 @@ static struct usb_serial_driver * const serial_drivers[] = {
 module_usb_serial_driver(serial_drivers, id_table);
 
 MODULE_DESCRIPTION(DRIVER_DESC);
-MODULE_LICENSE("GPL");
+MODULE_LICENSE("GPL v2");