iio: dac: ad5686: Add support for AD5337

AD5337 belongs to the same family as the AD5338.

The difference is that the AD5337 has 8-bit precision instead of 10-bit.

Add support for the AD5337 chip in the driver.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20221130182632.3856675-2-festevam@gmail.com


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