[MPS] Fix index_select scalar input with multiple indices (#91064)
Support operations like this:
```
device="mps"
arr = torch.tensor(10, device=device)
indices = torch.tensor([0, 0], device=device) # multiple indices
torch.index_select(arr, 0, indices)
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91064
Approved by: https://github.com/kulinseth
