iommu/dma: Remove __iommu_dma_free

We only have a single caller of this function left, so open code it there.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>