staging: comedi: ni_mio_common: open code the M-Series GPCT register offsets

Remove the enum m_series_register_offsets values that are only used in
the lookup tables for the GPCT to STC 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.

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>