dma-direct: remove the mapping_error dma_map_ops method

The dma-direct code already returns (~(dma_addr_t)0x0) on mapping
failures, so we can switch over to returning DMA_MAPPING_ERROR and let
the core dma-mapping code handle the rest.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/kernel/dma-swiotlb.c

@@ -59,7 +59,6 @@ const struct dma_map_ops powerpc_swiotlb_dma_ops = {
 	.sync_single_for_device = swiotlb_sync_single_for_device,
 	.sync_sg_for_cpu = swiotlb_sync_sg_for_cpu,
 	.sync_sg_for_device = swiotlb_sync_sg_for_device,
-	.mapping_error = dma_direct_mapping_error,
 	.get_required_mask = swiotlb_powerpc_get_required,
 };