staging: comedi: ni_tio: remove some dead code

These conditions can never be true because "i" is always one more than
NI_660X_MAX_RTSI_CHAN after the loop.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>