USB: serial: ti_usb_3410_5052: 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 port parameter is used to set the I/O port and does not make any
sense to use for USB serial devices.

The xmit_fifo_size parameter could be used to set the hardware transmit
fifo size of a legacy UART when it could not be detected, but the
interface is limited to eight bits and should be left unset when not
used.

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

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