staging: comedi: adl_pci9118: use comedi_fc helpers to validate timer args

Use the comedi_fc helper, cfc_check_trigger_arg_is(), to validate the
arguments for the TRIG_TIMER command sources. Pass the local variable to
i8253_cascade_ns_to_timer() instead of the cmd argument. This value
is modified by that function to return the actual time (in nanoseconds)
that the timer will be programmed with based on the calculated divisors.
The cfc_check_trigger_arg_is() helper will then validate that the argument
is that value and modify it if not.

Use cfc_check_trigger_arg_min() to do validate the cmd->scan_begin_arg
when the scan_begin_src is TRIG_TIMER and the convert_src is TRIG_NOW.

All the arguments are unsigned int, change the local variable to an
unsigned int and rename it for aesthetic reasons.

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>