x86: remove DMA_ERROR_CODE

All dma_map_ops instances now handle their errors through
->mapping_error.
Signed-off-by: NChristoph Hellwig <hch@lst.de>

arch/x86/include/asm/dma-mapping.h

@@ -19,8 +19,6 @@
 # define ISA_DMA_BIT_MASK DMA_BIT_MASK(32)
 #endif
 
-#define DMA_ERROR_CODE	0
-
 extern int iommu_merge;
 extern struct device x86_dma_fallback_dev;
 extern int panic_on_overflow;