[Bugfix][DispatchFFNCombine] resolve vec error caused by unaligned UB access (#6707)

### What this PR does / why we need it?
1. Fix a vec error caused by unaligned UB accesss in the
DispatchFFNCombine;
2. Fix expert_token_nums tensor defined on host instead of NPU in
moe_comm_method.py
3. Fix multi-core copy issue of expert_token_nums in dispatchffnCombine
op (single aiv copy is sufficient)

### Does this PR introduce _any_ user-facing change?

No, this PR does not introduce any user-facing changes. The fix only
addresses internal memory access logic and does not modify any public
APIs, interfaces, or user-visible behaviors.

### How was this patch tested?

`export VLLM_ASCEND_ENABLE_FUSED_MC2=1`

vLLM version: v0.15.0

- vLLM version: v0.15.0
- vLLM main:
9562912cea

Signed-off-by: xulei_ict <xulei292@huawei.com>
Co-authored-by: xulei_ict <xulei292@huawei.com>

csrc/dispatch_ffn_combine_bf16/op_kernel/dispatch_ffn_combine_bf16_kernel.hpp

@@ -756,8 +756,9 @@ CATLASS_DEVICE
         ExpertTokenNums.SetGlobalBuffer(reinterpret_cast<__gm__ int32_t*>(params.ptrExpertTokenNums));
         AscendC::GlobalTensor<int32_t> LcalCumsumMM;
         LcalCumsumMM.SetGlobalBuffer(reinterpret_cast<__gm__ int32_t*>(workspaceInfo.ptrcumsumMM + (params.EP - 1) * params.expertPerRank * sizeof(int32_t)));
-        CopyGMToGM(ExpertTokenNums, LcalCumsumMM, params.expertPerRank, params.ubMoveNum);
-        AscendC::SyncAll<true>();
+        if (coreIdx == 0) {
+            CopyGMToGM(ExpertTokenNums, LcalCumsumMM, params.expertPerRank, params.ubMoveNum);
+        }
 
         uint32_t curGroupOffset = 0;
         int32_t prevSumBeforeRank = 0;