### What this PR does / why we need it?
bugfix ascend schedule encountered an incorrect req block length in the
check_watermark_for_prefill function
### Does this PR introduce _any_ user-facing change?
### How was this patch tested?
- vLLM version: v0.10.1.1
- vLLM main:
426cc8629f
Signed-off-by: liziyu <liziyu16@huawei.com>