USB: serial: ftdi_sio: fix TIOCGSERIAL implementation

TIOCSSERIAL is a horrid, underspecified, legacy interface which for most
serial devices is only useful for setting the close_delay and
closing_wait parameters.

The FTDI driver is the only USB serial driver supporting the deprecated
ASYNC_SPD flags, which are reported back as they should by TIOCGSERIAL,
but the returned parameters did not include the line number.

The close_delay and closing_wait parameters returned by TIOCGSERIAL are
specified in centiseconds. The driver does not yet support changing
these, but let's report back the default values actually used (0.5 and
30 seconds, respectively).

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>