staging: comedi: ni_mio_common: tidy up the calibration subdevice init

For aesthetics, add some whitespace to the subdevice init.

Refactor the code so that the common parts of the subdevice are initialized
in one place.

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>