regulator: ad5398: Add device tree support

regulator: ad5398: Add device tree support

Previously, the ad5398 driver used only platform_data, which is
deprecated in favour of device tree. This caused the AD5398 to fail to
probe as it could not load its init_data. If the AD5398 has a device
tree node, pull the init_data from there using
of_get_regulator_init_data.

Signed-off-by: Isaac Scott <isaac.scott@ideasonboard.com>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Link: https://patch.msgid.link/20250128173143.959600-4-isaac.scott@ideasonboard.com
Signed-off-by: Mark Brown <broonie@kernel.org>