iio: adc: ad9467: use DMA safe buffer for spi

iio: adc: ad9467: use DMA safe buffer for spi

Make sure we use a DMA safe buffer (IIO_DMA_MINALIGN) for all the spi
transfers. Only relevant for writes since for reads
spi_write_then_read() is used which does not require DMA safe buffers.

Also note that for consistency, ad9467_spi_read() is also taking struct
ad9467_state as a parameter (even if not really needed).

Fixes: ad6797120238 ("iio: adc: ad9467: add support AD9467 ADC")
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240522-dev-ad9467-dma-v2-1-a37bec463632@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>