bugfix: fix initialization error for mooncake in k8s (#2541)

### What this PR does / why we need it?
The detail has been clarified in that issue :
https://github.com/vllm-project/vllm-ascend/issues/2557

### Does this PR introduce _any_ user-facing change?
NO

### How was this patch tested?
easy to test beacause we just need to echo the variable


- vLLM version: v0.10.1.1
- vLLM main:
6997a25ac6

---------

Signed-off-by: zzy-ContiLearn <1831242919@qq.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: LCAIZJ <leichao139636@163.com>

vllm_ascend/envs.py

@@ -135,6 +135,10 @@ env_variables: Dict[str, Callable[[], Any]] = {
     # this feature in eager mode will get better performance.
     "VLLM_ASCEND_ENABLE_MLP_OPTIMIZE":
     lambda: bool(int(os.getenv("VLLM_ASCEND_ENABLE_MLP_OPTIMIZE", '0'))),
+    # Determine the number of physical devices in a non-full-use scenario
+    # caused by the initialization of the Mooncake connector.
+    "PHYSICAL_DEVICES":
+    lambda: os.getenv("PHYSICAL_DEVICES", None),
 }
 
 # end-env-vars-definition