iio: adc: ti-adc081c: use individual model structures instead of array

iio: adc: ti-adc081c: use individual model structures instead of array

Change the ti-adc081c driver to use individual model structures instead
of an array. This reduces the verbosity of the code. Also, the data is
now const as it should have been in the first place. The ADCxx1C_MODEL()
macro is dropped to be consistent with similar model definitions in
other drivers.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250721-iio-const-data-11-v2-1-c3fec12511ee@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>