### What this PR does / why we need it?
It's a tiny bugfix in the `gen_ranktable.py` script. The script is an
util to help setup an example case. It is used to prepare a ranktable
before disaggregated prefill deployment.
Elements in `local_device_ids` list should be casted to `int` type
before referred for a MOD math operation.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
No.
- vLLM version: v0.11.0
- vLLM main:
c9461e05a4
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Signed-off-by: paulyu12 <507435917@qq.com>
b8796b06c8