iio: adc: ad7949: Fix alignment for DMA safety

iio: adc: ad7949: Fix alignment for DMA safety

____cacheline_aligned is an insufficient guarantee for non-coherent DMA
on platforms with 128 byte cachelines above L1.  Switch to the updated
IIO_DMA_MINALIGN definition.

Note the fixes tag predates some changes to this line of code so
automated application of this fix may fail.

Fixes: 03a6ee446985 ("iio:adc:ad7949: Add AD7949 ADC driver family")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Charles-Antoine Couret <charles-antoine.couret@essensium.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-20-jic23@kernel.org