Fix multiline signatures in docstring (#38768)
Summary:
Fix https://github.com/pytorch/pytorch/issues/38694
See https://5533621-65600975-gh.circle-artifacts.com/0/docs/torch.html
## Index Page
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## Detail Page
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Pull Request resolved: https://github.com/pytorch/pytorch/pull/38768
Differential Revision: D21691859
Pulled By: zou3519
fbshipit-source-id: 336158be450436554a1fa2105a5eedf24236c56b
