Correct the type of some floating point literals in calc_digamma (#42846)
Summary:
They are double, but they are supposed to be of accscalar_t or a faster type.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42846
Reviewed By: zou3519
Differential Revision: D23049405
Pulled By: mruberry
fbshipit-source-id: 29bb5d5419dc7556b02768f0ff96dfc28676f257
