[booster] torch fsdp fix ckpt

[wukong1992]

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The code coverage for the changed files is %.

Click me to view the complete report

Name                                                        Stmts   Miss  Cover
-------------------------------------------------------------------------------
colossalai/booster/booster.py                                  63     10    84%
colossalai/booster/plugin/torch_fsdp_plugin.py                 93     12    87%
colossalai/checkpoint_io/general_checkpoint_io.py              69      7    90%
tests/test_booster/test_plugin/test_torch_fsdp_plugin.py       43      0   100%
tests/test_checkpoint_io/test_torch_fsdp_checkpoint_io.py      83      6    93%
-------------------------------------------------------------------------------
TOTAL                                                         351     35    90%