s390/dma: provide dma_cache_sync() function

Provide empty dma_cache_sync() function.
Acked-by: NSebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

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

@@ -20,8 +20,11 @@ static inline struct dma_map_ops *get_dma_ops(struct device *dev)
 
 extern int dma_set_mask(struct device *dev, u64 mask);
 extern int dma_is_consistent(struct device *dev, dma_addr_t dma_handle);
-extern void dma_cache_sync(struct device *dev, void *vaddr, size_t size,
-			   enum dma_data_direction direction);
+
+static inline void dma_cache_sync(struct device *dev, void *vaddr, size_t size,
+				  enum dma_data_direction direction)
+{
+}
 
 #define dma_alloc_noncoherent(d, s, h, f) dma_alloc_coherent(d, s, h, f)
 #define dma_free_noncoherent(d, s, v, h) dma_free_coherent(d, s, v, h)