iio: proximity: as3935: 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.

Fixes: 24ddb0e4 ("iio: Add AS3935 lightning sensor support")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Matt Ranostay <mranostay@gmail.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-87-jic23@kernel.org

drivers/iio/proximity/as3935.c

@@ -65,7 +65,7 @@ struct as3935_state {
 		u8 chan;
 		s64 timestamp __aligned(8);
 	} scan;
-	u8 buf[2] ____cacheline_aligned;
+	u8 buf[2] __aligned(IIO_DMA_MINALIGN);
 };
 
 static const struct iio_chan_spec as3935_channels[] = {