arm64: remove DMA_ERROR_CODE

The dma alloc interface returns an error by return NULL, and the
mapping interfaces rely on the mapping_error method, which the dummy
ops already implement correctly.

Thus remove the DMA_ERROR_CODE define.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>

arch/arm64/include/asm/dma-mapping.h

@@ -24,7 +24,6 @@
 #include <xen/xen.h>
 #include <asm/xen/hypervisor.h>
 
-#define DMA_ERROR_CODE	(~(dma_addr_t)0)
 extern const struct dma_map_ops dummy_dma_ops;
 
 static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)

arch/arm64/mm/dma-mapping.c

@@ -184,7 +184,6 @@ static void *__dma_alloc(struct device *dev, size_t size,
 no_map:
 	__dma_free_coherent(dev, size, ptr, *dma_handle, attrs);
 no_mem:
-	*dma_handle = DMA_ERROR_CODE;
 	return NULL;
 }
 
@@ -487,7 +486,7 @@ static dma_addr_t __dummy_map_page(struct device *dev, struct page *page,
 				   enum dma_data_direction dir,
 				   unsigned long attrs)
 {
-	return DMA_ERROR_CODE;
+	return 0;
 }
 
 static void __dummy_unmap_page(struct device *dev, dma_addr_t dev_addr,