USB: mos7840: fix tiocmget error handling

Make sure to return errors from tiocmget rather than rely on
uninitialised stack data.

Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/mos7840.c

@@ -1532,7 +1532,11 @@ static int mos7840_tiocmget(struct tty_struct *tty)
 		return -ENODEV;
 
 	status = mos7840_get_uart_reg(port, MODEM_STATUS_REGISTER, &msr);
+	if (status != 1)
+		return -EIO;
 	status = mos7840_get_uart_reg(port, MODEM_CONTROL_REGISTER, &mcr);
+	if (status != 1)
+		return -EIO;
 	result = ((mcr & MCR_DTR) ? TIOCM_DTR : 0)
 	    | ((mcr & MCR_RTS) ? TIOCM_RTS : 0)
 	    | ((mcr & MCR_LOOPBACK) ? TIOCM_LOOP : 0)