generate.py bug: using global var args.prompt instead of prompt passed to the method

[meirm]

The script generate.py in the subdir llms/hf_llm has a bug where it uses the global var args.prompt instead of prompt as passed to the method. This causes the script to generate incorrect results. The bug should be fixed to ensure the correctness of the script.

[awni]

Sorry about that, the fix is in #227