### What this PR does / why we need it?
The code bug caused an empty bubble. When the npu_paged_cache_load
operator was called, it forcibly transferred seq_len2 to the device,
which triggered synchronization and interrupted the CPU operator's
launch stream.
- vLLM version: v0.11.0
- vLLM main:
83f478bb19
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Signed-off-by: underfituu <hzhucong@163.com>