autodiff fix for autocast_to_xxx (#67648)
Summary:
Fixes autocast + autodiff issue where `RuntimeError: grad_inputs.size() == node->inputs().size()INTERNAL ASSERT FAILED at "../torch/csrc/jit/runtime/autodiff.cpp":426, please report a bug to PyTorch.`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67648
Reviewed By: cpuhrsch
Differential Revision: D32083227
Pulled By: davidberard98
fbshipit-source-id: edf526cff4ec21874ae35ec730d13c250073e10c
