USB: mos7840: remove unused variable

Fix warning about unused variable introduced by commit e681b66f
("USB: mos7840: remove invalid disconnect handling") upstream.

A subsequent fix which removed the disconnect function got rid of the
warning but that one was only backported to v3.6.
Reported-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/serial/mos7840.c

@@ -2585,7 +2585,6 @@ static int mos7840_startup(struct usb_serial *serial)
 static void mos7840_disconnect(struct usb_serial *serial)
 {
 	int i;
-	unsigned long flags;
 	struct moschip_port *mos7840_port;
 	dbg("%s", " disconnect :entering..........");