[ROCm] work around compiler issue for IGammaKernel.cu (#50970)
Summary:
Add const to static variable inside `__host__ __device__` function.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50970
Reviewed By: izdeby
Differential Revision: D26081478
Pulled By: heitorschueroff
fbshipit-source-id: 77cf145f7e0570359aa00aec4c8b82c950815f81
