[PATCH -next] dma-mapping: Fix build error unused-value

[Ren Zhijie]

If CONFIG_DMA_DECLARE_COHERENT is not set,
make ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- will be failed, like this:

drivers/remoteproc/remoteproc_core.c: In function ‘rproc_rvdev_release’:
./include/linux/dma-map-ops.h:182:42: error: statement with no effect [-Werror=unused-value]
 #define dma_release_coherent_memory(dev) (0)
                                          ^
drivers/remoteproc/remoteproc_core.c:464:2: note: in expansion of macro ‘dma_release_coherent_memory’
  dma_release_coherent_memory(dev);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

The return type of function dma_release_coherent_memory in CONFIG_DMA_DECLARE_COHERENT area is void, so in !CONFIG_DMA_DECLARE_COHERENT area it should neither return any value nor be defined as zero.

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Fixes: e61c451476e6("dma-mapping: Add dma_release_coherent_memory to DMA API")
Signed-off-by: Ren Zhijie <renzhijie2@xxxxxxxxxx>
---
 include/linux/dma-map-ops.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index 53db9655efe9..bfffe494356a 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -179,10 +179,10 @@ static inline int dma_declare_coherent_memory(struct device *dev,
 	return -ENOSYS;
 }
 
-#define dma_release_coherent_memory(dev) (0)
 #define dma_alloc_from_dev_coherent(dev, size, handle, ret) (0)
 #define dma_release_from_dev_coherent(dev, order, vaddr) (0)
 #define dma_mmap_from_dev_coherent(dev, vma, vaddr, order, ret) (0)
+static inline void dma_release_coherent_memory(struct device *dev) { }
 #endif /* CONFIG_DMA_DECLARE_COHERENT */
 
 #ifdef CONFIG_DMA_GLOBAL_POOL
-- 
2.17.1