iio: dac: ad3552r: changes to use FIELD_PREP

Changes to use FIELD_PREP, so that driver-specific ad3552r_field_prep
is removed. Variables (arrays) that was used to call ad3552r_field_prep
are removed too.

Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20241028-wip-bl-ad3552r-axi-v0-iio-testing-v9-5-f6960b4f9719@kernel-space.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>