USB: serial: ftdi_sio: fix 300 bps rate for SIO

The 300 bps rate of SIO devices has been mapped to 9600 bps since
2003... Let's fix the regression.

Cc: stable@vger.kernel.org
Signed-off-by: NJohan Hovold <johan@kernel.org>

drivers/usb/serial/ftdi_sio.c

@@ -1319,8 +1319,7 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
 		case 38400: div_value = ftdi_sio_b38400; break;
 		case 57600: div_value = ftdi_sio_b57600;  break;
 		case 115200: div_value = ftdi_sio_b115200; break;
-		} /* baud */
-		if (div_value == 0) {
+		default:
 			dev_dbg(dev, "%s - Baudrate (%d) requested is not supported\n",
 				__func__,  baud);
 			div_value = ftdi_sio_b9600;