USB: kobil_sct: use port interrupt-out urb

Use the port interrupt-out urb rather than abusing the port write_urb
pointer and allocating a new urb at every open (but the first...).

Note that the write_urb abuse would have led to a double free should
there ever be interfaces with a bulk-out endpoint.

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