iio: adc: ad7476: Simplify chip type detection

iio: adc: ad7476: Simplify chip type detection

The ad7476 driver uses a table of structures for defining the IC variant
specific data. Table is indexed using enum values, which are picked by
SPI ID.

Having the table and an enum adds extra complexity and may encourage
adding IC specific quircks in the code, instead of centralizing the IC
differences in one place, the chip-info.

Simplify this by dropping the table and using individual structures for
the IC specific data, and storing the IC specific structure's address
directly in the SPI ID data. Finally, switch to the
spi_get_device_match_data() and add a check for the return value.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://patch.msgid.link/9e179bb3ba52303448ae4a559c1f011acd3f2fa6.1754901948.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>