iio: dac: ad5791: fix storage

iio: dac: ad5791: fix storage

IIO uses "natural" alignment so storagebits should always be a power of
2. Change storagebits to 32 since that is the natural size to store 24
bits of data.

The ad5791 driver currently doesn't use this field anywhere and doesn't
support buffered writes, so this does not change anything. We just don't
want anyone to think that it is OK to have storagebits = 24 in other
drivers.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250122-iio-dac-ad5791-fix-storagebits-v1-1-53746e0f25cd@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>