arm64: default to the direct mapping in get_arch_dma_ops

arm64: default to the direct mapping in get_arch_dma_ops

Otherwise the direct mapping won't work at all given that a NULL
dev->dma_ops causes a fallback.  Note that we already explicitly set
dev->dma_ops to dma_dummy_ops for dma-incapable devices, so this
fallback should not be needed anyway.

Fixes: 356da6d0cd ("dma-mapping: bypass indirect calls for dma-direct")
Signed-off-by: Christoph Hellwig <[email protected]>
Reported-by: Marek Szyprowski <[email protected]>
Tested-by: Marek Szyprowski <[email protected]>
Reviewed-by: Robin Murphy <[email protected]>