staging: iio: resolver: ad2s1210: always use 16-bit value for raw read

staging: iio: resolver: ad2s1210: always use 16-bit value for raw read

This removes the special handling for resolutions lower than 16 bits.
This will allow us to use a fixed scale independent of the resolution.

A new sample field is added to store the raw data instead of reusing
the config mode rx buffer so that we don't have to do a cast or worry
about unaligned access.

Also, for the record, according to the datasheet, the logic for the
special handling based on hysteresis that was removed was incorrect.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20230929-ad2s1210-mainline-v3-7-fa4364281745@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>