[misc] fix debugging code (vllm-project#13487)

Signed-off-by: youkaichao <[email protected]>

docs/source/getting_started/troubleshooting.md

@@ -94,20 +94,20 @@ pynccl.disabled = False
 s = torch.cuda.Stream()
 with torch.cuda.stream(s):
     data.fill_(1)
-    pynccl.all_reduce(data, stream=s)
-    value = data.mean().item()
+    out = pynccl.all_reduce(data, stream=s)
+    value = out.mean().item()
     assert value == world_size, f"Expected {world_size}, got {value}"
 
 print("vLLM NCCL is successful!")
 
 g = torch.cuda.CUDAGraph()
 with torch.cuda.graph(cuda_graph=g, stream=s):
-    pynccl.all_reduce(data, stream=torch.cuda.current_stream())
+    out = pynccl.all_reduce(data, stream=torch.cuda.current_stream())
 
 data.fill_(1)
 g.replay()
 torch.cuda.current_stream().synchronize()
-value = data.mean().item()
+value = out.mean().item()
 assert value == world_size, f"Expected {world_size}, got {value}"
 
 print("vLLM NCCL with cuda graph is successful!")