iio: magn: st_magn: inline per-sensor data

We have #defines for all the individual sensor registers and
value/mask pairs #defined at the top of the file and used at
exactly one spot.

This is usually good if the #defines give a meaning to the
opaque magic numbers.

However in this case, the semantic meaning is inherent in the
name of the C99-addressable fields, and that means duplication
of information, and only makes the code hard to maintain since
you every time have to add a new #define AND update the site
where it is to be used.

Get rid of the #defines and just open code the values into the
appropriate struct elements. Make sure to explicitly address
the .hz and .value fields in the st_sensor_odr_avl struct
so that the meaning of all values is clear.

This patch is purely syntactic should have no semantic effect.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>