iio: dac: ad8460: add SPI device match table

Add SPI device match table for ADI AD8460 DAC. As described in [1], this
is required for the module to automatically load, even when using DT.

[1]: https://lore.kernel.org/all/20210921192149.50740-1-broonie@kernel.org/



Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20241018-iio-dac-ad8460-add-spi-match-table-v1-1-84a5f903bf50@baylibre.com


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