staging: comedi: pcl812: convert hardware type defines into an enum

For aesthetics, convert these defines into an enum and rename the
CamelCase. Fix the switch() code to use the enum without warnings.

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>