Fix distributed store to use add for the counter of DL shared seed (#80348)
In order to get the result of `_shared_seed_recv_cnt` properly, switch from `store.get` to `store.add(key, 0)`.
See the comment from distributed team for the reason:
https://github.com/pytorch/pytorch/blob/590d3e5774110e4657dcaa6acdb387ef69e41b47/torch/distributed/distributed_c10d.py#L242-L246
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80348
Approved by: https://github.com/VitalyFedyunin, https://github.com/NivekT
