[Bug] vl_async_engine中存在一个拼写错误

### Checklist

- [X] 1. I have searched related issues but cannot get the expected help.
- [X] 2. The bug has not been fixed in the latest version.
- [X] 3. Please note that if the bug-related issue you submitted lacks corresponding environment info and a minimal reproducible demo, it will be challenging for us to reproduce and resolve the issue, reducing the likelihood of receiving feedback.

### Describe the bug

https://github.com/InternLM/lmdeploy/blob/main/lmdeploy/serve/vl_async_engine.py#L127
存在一个拼写错误，应该是system而不是sytem

### Reproduction

None

### Environment

```Shell
None
```

### Error traceback

_No response_