Fix typo when setting FSDP state dict config (#97110)
`get_state_dict_type` in FSDP looks for a key called `_optim_state_dict_config` when getting the optimizer state dict config. However, `set_state_dict_type` sets the config at a key called `_optimstate_dict_config`. This looks like a typo.
This fixes the discrepancy, so that when you set the state dict type, it is correctly used.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97110
Approved by: https://github.com/awgu, https://github.com/fegin
