Fix type error in `ZeROOrderedDict` (#6794)
As @keskival pointed in
https://github.com/microsoft/DeepSpeed/commit/3d5cf739ead7c78f518a518ccaa15a323bd5c8da#r149582004,
I've confirmed there's a type error, which this PR fixes.
I didn't run into this because our internal version still use `*r2`.
Co-authored-by: Tero Keski-Valkama <tero.keskivalkama@gmail.com>
Co-authored-by: Logan Adams <114770087+loadams@users.noreply.github.com>