USB: serial: io_ti: bind to interface after fw download

Bind to the interface, but do not register any ports, after having
downloaded the firmware. The device will still disconnect and
re-enumerate, but this way we avoid an error messages from being logged
as part of the process:

io_ti: probe of 1-1.3:1.0 failed with error -5

Signed-off-by: Johan Hovold <johan@kernel.org>