staging:iio:adc:ad7280a: Register define cleanup.

1. Postfix register addresses with _REG to distinguish them from
   fields within the registers
2. Switch to using FIELD_PREP and masks to aid readability.
3. Shorten a few defines to make the lines remain a sensible length.
4. Fix an issue whether where an CTRL_LB field is set in CTRL_HB.
5. Fix wrong AUX1_3_4 which should be AUX_1_3_5 according to
   table 14 in the datasheet.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Marcelo Schmitt <marcelo.schmitt1@gmail.com>
Link: https://lore.kernel.org/r/20220206190328.333093-3-jic23@kernel.org