sh: remove DMA_ERROR_CODE

sh does not return errors for dma_map_page.
Signed-off-by: NChristoph Hellwig <hch@lst.de>

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

@@ -9,8 +9,6 @@ static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
 	return dma_ops;
 }
 
-#define DMA_ERROR_CODE 0
-
 void dma_cache_sync(struct device *dev, void *vaddr, size_t size,
 		    enum dma_data_direction dir);