staging: comedi: ni_tio: fix ni_tio_insn_config()

The (*insn_config) functions are supposed to return an errno or the number
of 'data' values used for the instruction (insn->n). Currently this function
returns an errno or 0. Fix the function to work like the core expects.

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