USB: serial: kobil_sct: mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Addresses-Coverity-ID: 115014
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: NJohan Hovold <johan@kernel.org>

drivers/usb/serial/kobil_sct.c

@@ -491,6 +491,7 @@ static void kobil_set_termios(struct tty_struct *tty,
 		break;
 	default:
 		speed = 9600;
+		/* fall through */
 	case 9600:
 		urb_val = SUSBCR_SBR_9600;
 		break;