microblaze: remove DMA_ERROR_CODE

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

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

@@ -28,8 +28,6 @@
 #include <asm/io.h>
 #include <asm/cacheflush.h>
 
-#define DMA_ERROR_CODE		(~(dma_addr_t)0x0)
-
 #define __dma_alloc_coherent(dev, gfp, size, handle)	NULL
 #define __dma_free_coherent(size, addr)		((void)0)