arm64: dma-mapping: Fix dma_mapping_error() when bypassing SWIOTLB

arm64: dma-mapping: Fix dma_mapping_error() when bypassing SWIOTLB

BugLink: http://bugs.launchpad.net/bugs/1672544
commit adbe7e26f4257f72817495b9bce114284060b0d7 upstream.

When bypassing SWIOTLB on small-memory systems, we need to avoid calling
into swiotlb_dma_mapping_error() in exactly the same way as we avoid
swiotlb_dma_supported(), because the former also relies on SWIOTLB state
being initialised.

Under the assumptions for which we skip SWIOTLB, dma_map_{single,page}()
will only ever return the DMA-offset-adjusted physical address of the
page passed in, thus we can report success unconditionally.

Fixes: b67a8b29df7e ("arm64: mm: only initialize swiotlb when necessary")
CC: Jisheng Zhang <jszhang@marvell.com>
Reported-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>