### What this PR does / why we need it? - Fix `AssertionError` of `weight_prefetch_method` in W8A8 MTP scene - Remove hard-code key (https://github.com/vllm-project/vllm-ascend/pull/3146#discussion_r2416644010) ### Does this PR introduce _any_ user-facing change? None ### How was this patch tested? `weight_prefetch_method is None` (tested on DeepSeek-R1-w8a8mix_MTP) - vLLM version: v0.11.0rc3 - vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0 Signed-off-by: zhoux77899 <zhouxiang100@huawei.com>