### What this PR does / why we need it?
Fix incorrect MLAPO weight release in PD mixex scenarios.
### Does this PR introduce _any_ user-facing change?
### How was this patch tested?
- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c
Signed-off-by: ZYang6263 <zy626375@gmail.com>
Co-authored-by: wangxiyuan <wangxiyuan1007@gmail.com>