staging: comedi: ni_mio_common: open code the M-Series regmap offsets

Remove the enum m_series_register_offsets values that are only used in
the lookup tables for the STC to M-Series register mapping and just open
code the values. Having the extra level of indirection does not add any
additional clarity and it gets rid of some of the CamelCase symbols.

Some of the registers are not currently used by the driver so the mappings
were not present in the original switch code. Add the missing register
mappings to the lookup tables.

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>