dma-buf: cleanup dma_fence_chain_walk

Use unrcu_pointer() instead of the manual cast.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220518085446.31338-1-christian.koenig@amd.com

drivers/dma-buf/dma-fence-chain.c

@@ -62,8 +62,8 @@ struct dma_fence *dma_fence_chain_walk(struct dma_fence *fence)
 			replacement = NULL;
 		}
 
-		tmp = cmpxchg((struct dma_fence __force **)&chain->prev,
-			      prev, replacement);
+		tmp = unrcu_pointer(cmpxchg(&chain->prev, RCU_INITIALIZER(prev),
+					     RCU_INITIALIZER(replacement)));
 		if (tmp == prev)
 			dma_fence_put(tmp);
 		else