Fix fdsp config in cluster

[muellerzr]

fsdp_config doesn't have a default None value and will raise an issue if you aren't using DistributedType.MULTI_GPU

Traceback (most recent call last):
  File "/opt/conda/bin/accelerate", line 8, in <module>
    sys.exit(main())
  File "/opt/conda/lib/python3.8/site-packages/accelerate/commands/accelerate_cli.py", line 43, in main
    args.func(args)
  File "/opt/conda/lib/python3.8/site-packages/accelerate/commands/config/__init__.py", line 64, in config_command
    config = get_user_input()
  File "/opt/conda/lib/python3.8/site-packages/accelerate/commands/config/__init__.py", line 37, in get_user_input
    config = get_cluster_input()
  File "/opt/conda/lib/python3.8/site-packages/accelerate/commands/config/cluster.py", line 165, in get_cluster_input
    fsdp_config=fsdp_config,
UnboundLocalError: local variable 'fsdp_config' referenced before assignment

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Thanks for fixing!