s390: remove the unused dma_capable helper

Signed-off-by: Christoph Hellwig <hch@lst.de>

arch/s390/include/asm/dma-mapping.h

@@ -16,11 +16,4 @@ static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
 	return &dma_noop_ops;
 }
 
-static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size)
-{
-	if (!dev->dma_mask)
-		return false;
-	return addr + size - 1 <= *dev->dma_mask;
-}
-
 #endif /* _ASM_S390_DMA_MAPPING_H */