These days all devices should have a DMA coherent mask, and most dma_ops
implementations rely on that fact.  But just to be sure add an assert to
ring the warning bell if that is not the case.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NVladimir Murzin <vladimir.murzin@arm.com>
Reviewed-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>