staging: comedi: ni_labpc_common: use the cfc_check_trigger_arg_*() helpers

For aesthetics, use the helper functions to check the min/max divisor values.
Remove the const int local variables and open code the values.

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>