[Python] Fix BOOL error in logit processor.

[simpolism]

Was getting this error with mlc_llm serve via cpu:

error: BOOL
 --> /home/jake/github/mlc/models/.venv/lib/python3.10/site-packages/mlc_llm/compiler_pass/attach_logit_processor.py:148:21
     |
 148 |                      logits[seq_ids[pos2seq_id[vp]], token_ids[vp]] < 0,
     |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Similar to this issue with TVM (apache/tvm#18578).

My PR casts 0 into a proper tvm type via T.float32.