staging: comedi: ni_mio_common: remove forward declaration 8

Move the cs5529 calibration subdevice functions and helpers 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>