swiotlb: remove the overflow buffer

Like all other dma mapping drivers just return an error code instead
of an actual memory buffer.  The reason for the overflow buffer was
that at the time swiotlb was invented there was no way to check for
dma mapping errors, but this has long been fixed.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/powerpc/kernel/dma-swiotlb.c

@@ -11,7 +11,7 @@
  *
  */
 
-#include <linux/dma-mapping.h>
+#include <linux/dma-direct.h>
 #include <linux/memblock.h>
 #include <linux/pfn.h>
 #include <linux/of_platform.h>
@@ -59,7 +59,7 @@ 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 = swiotlb_dma_mapping_error,
+	.mapping_error = dma_direct_mapping_error,
 	.get_required_mask = swiotlb_powerpc_get_required,
 };