iommu/dma: don't rely on DMA_ERROR_CODE

DMA_ERROR_CODE is not a public API and will go away soon.  dma dma-iommu
driver already implements a proper ->mapping_error method, so it's only
using the value internally.  Add a new local define using the value
that arm64 which is the only current user of dma-iommu.

Signed-off-by: Christoph Hellwig <hch@lst.de>