USB: io_ti: fix TIOCGSERIAL

Fix regression introduced by commit f40d7815 ("USB: io_ti: kill custom
closing_wait implementation") which made TIOCGSERIAL return the wrong
value for closing_wait.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Cc: stable <stable@vger.kernel.org> # 3.9
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>