Remove unhandled switch case fall-through in MSCCL

[corey-derochie-amd]

Details

Do not mention proprietary info or link to internal work items in this PR.

Work item: #1254

What were the changes?
Added missing break in switch case.

Why were the changes made?
Switch case was falling through unhandled.

Additional Documentation:
Need to determine if this fall-through was intentional.

Approval Checklist

Do not approve until these items are satisfied.

• [ ] Verify the CHANGELOG has been updated, if
  • there are any NCCL API version changes,
  • any changes impact library users, and/or
  • any changes impact any other ROCm library.