### What this PR does / why we need it?
After enabling Mlapo and DCP, since Mlapo has its own mla_preprocess
logic and does not perform additional all_gather operations on the DCP
group, this will lead to dimension mismatch during the subsequent
forward proces
### Does this PR introduce _any_ user-facing change?
N/A
- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c
Signed-off-by: zengran <zengran2@huawei.com>
Co-authored-by: wangxiyuan <wangxiyuan1007@gmail.com>