dma-buf: cleanup dma_fence_chain_walk

Use unrcu_pointer() instead of the manual cast.

Signed-off-by: Christian König <[e-mail]>
Reviewed-by: Daniel Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

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

···
 			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