Fix compiler warning for MathConstants.h (#52123)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52123
Compiler currently complains:
```
caffe2/c10/util/MatchConstants.h(18): warning: calling a constexpr __host__ function("from_bits") from a __host__ __device__ function("pi") is not allowed.
```
This diff extirpates the warning
Test Plan: Sandcastle tests
Reviewed By: xush6528
Differential Revision: D26379485
fbshipit-source-id: ab4821119cba8c43fd1d5788c4632d0613529ec8
