staging: comedi: comedi_fc.h: introduce new helpers for do_cmdtest step 3

staging: comedi: comedi_fc.h: introduce new helpers for do_cmdtest step 3

Step 3 of the do_cmdtest functions validates the arguments for the
command to be executed. Most of these are simple tests to see if the
argument "is" a value, a "min" value, or a "max" value. Each of these
tests then clamps the argument to the value if it fails the test.

Introduce three new helper functions in comedi_fc.h to handle these
tests and remove the boilerplate code from the drivers.

The new helper functions are:

cfc_check_trigger_arg_is()  - argument must be == the value
cfc_check_trigger_arg_min() - argument must be >= the value
cfc_check_trigger_arg_max() - argument must be <= the value

All of these helpers set the argument to the value and return -EINVAL
if the validation fails.

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