iio: adc: aspeed: Keep model data to driver data.

Keep the model data pointer to driver data for reducing the usage of
of_device_get_match_data().

Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
Link: https://lore.kernel.org/r/20210922081520.30580-2-billy_tsai@aspeedtech.com


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