### What this PR does / why we need it?
Fix accuracy issue on prefix caching with AscendScheduler
### How was this patch tested?
CI passed with `test_prefix_cache_with_ascend_scheduler`
- vLLM version: v0.10.1.1
- vLLM main:
6997a25ac6
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Signed-off-by: MengqingCao <cmq0113@163.com>