iommu/dma: Apply dma_{alloc,free}_contiguous functions

This patch replaces dma_{alloc,release}_from_contiguous() with
dma_{alloc,free}_contiguous() to simplify those function calls.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>