staging: comedi: ni_mio_common: remove forward declaration 3

Move the pwm config functions to remove the need for the forward
declarations.

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>