Updated fused_kernels import path

[Yazeed7]

Model conversion scripts in tools/checkpoint fail after the refactor with the following error:

Traceback (most recent call last):
  File "Megatron-LM/tools/checkpoint/convert.py", line 155, in <module>
    main()
  File "Megatron-LM/tools/checkpoint/convert.py", line 148, in main
    loader.load_checkpoint(queue, args)
  File "Megatron-LM/tools/checkpoint/loader_llama2_hf.py", line 361, in load_checkpoint
    _load_checkpoint(queue, args)
  File "Megatron-LM/tools/checkpoint/loader_llama2_hf.py", line 166, in _load_checkpoint
    from megatron.training import fused_kernels
ImportError: cannot import name 'fused_kernels' from 'megatron.training' (Megatron-LM/megatron/training/__init__.py)

I updated the import paths to fused_kernels, which solved this issue.