[Bugfix][CPU] Fix cpu all-reduce using native pytorch implementation (vllm-project#13586)

Author: Isotr0py

vllm/distributed/device_communicators/cpu_communicator.py

@@ -30,4 +30,5 @@ def __init__(self,
             pass
 
     def all_reduce(self, input_):
-        return self.dist_module.all_reduce(input_, group=self.device_group)
+        self.dist_module.all_reduce(input_, group=self.device_group)
+        return input_