one liner DMA mapping fix for 4.20

Hi Linus,

I'm sending this directly to you given how late we are. This is a trivial one liner fixing a regression I introduces in this merge merge, and which has only been noticed by code inspection, but which is pretty obvious when looking at the original commit. It would be great if it could make 4.20.

We really need the writecombine flag in dma_alloc_wc, fix a stupid oversight.

---
 include/linux/dma-mapping.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 15bd41447025..d327bdd53716 100644
@@ -796,7 +796,7 @@ static inline void dmam_release_declared_memory(struct device *dev)
 static inline void *dma_alloc_wc(struct device *dev, size_t size,
 				 dma_addr_t *dma_addr, gfp_t gfp)
 {
-	unsigned long attrs = DMA_ATTR_NO_WARN;
+	unsigned long attrs = DMA_ATTR_WRITE_COMBINE;
 
 	if (gfp & __GFP_NOWARN)
 		attrs |= DMA_ATTR_NO_WARN;

2.19.2