iio: temp: maxim_thermocouple: 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: 1f25ca11 ("iio: temperature: add support for Maxim thermocouple chips")
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/20220508175712.647246-93-jic23@kernel.org