iio: proximity: vcnl3020: add DMA safe buffer

Add DMA safe buffer for bulk transfers.

Signed-off-by: Ivan Mikhaylov <i.mikhaylov@yadro.com>
Link: https://lore.kernel.org/r/20210722154420.915082-2-i.mikhaylov@yadro.com


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