[EPLB] Eplb Verify Fix (#4333)

### What this PR does / why we need it?
Eplb Verify Fix

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

### How was this patch tested?

- vLLM version: v0.11.0
- vLLM main:
2918c1b49c

---------

Signed-off-by: shenchuxiaofugui <1311027364@qq.com>
Signed-off-by: LI SHENGYONG <49200266+shenchuxiaofugui@users.noreply.github.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

vllm_ascend/ops/fused_moe/fused_moe.py

@@ -257,7 +257,8 @@ class AscendFusedMoE(FusedMoE):
                                         dtype=torch.int64).npu()
 
         eplb_enable = self.dynamic_eplb or (self.expert_map_path is not None)
-        if eplb_enable and (not isinstance(self.quant_method,
+        if eplb_enable and (not hasattr(self.quant_method, "quant_method") or
+                            not isinstance(self.quant_method.quant_method,
                                            AscendW8A8DynamicFusedMoEMethod)):
             raise ValueError("Eplb supports only w8a8_dynamic quantization.")