staging: comedi: adv_pci1710: use comedi_fc helpers to validate timer args

staging: comedi: adv_pci1710: use comedi_fc helpers to validate timer args

Use the comedi_fc helper, cfc_check_trigger_arg_is(), to validate the
cmd->convert_arg for the convert_src TRIG_TIMER. 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
cmd->convert_arg is that value and modify it if not.

The minimum validation is not needed. That was already handled in Step 3.

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>