[FSDP][Easy] Rename `entry` -> `fsdp_module` to be more descriptive (#90864)
I started refactoring unit tests to use `_get_fsdp_states()` instead of `FullyShardedDataParallel.fsdp_modules()` but realized we should not do that for now. This is just a change I made while doing that. `entry` is not descriptive. Let us explicitly say `fsdp_module`. `for fsdp_module in FSDP.fsdp_modules(module)` is a proper idiom.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90864
Approved by: https://github.com/rohan-varma
