staging: comedi: addi_apci_3120: board does not have ttl i/o

The boards supported by this driver do not have ttl i/o. Remove
the unnecessary code to initialize the subdevice.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>