[Easy] Reuse `source` variable in `wrap_tensor` (#98845)
https://github.com/pytorch/pytorch/blob/2fab2893aa7b255127e0b92560585d9ecf6dc506/torch/_dynamo/variables/builder.py#L759-L760
We already save `source = self.get_source()` to begin `wrap_tensor()`. Since the source should be fixed at `VariableBuilder` construction time, we should be okay to reuse the `source` variable instead of calling `get_source()` every time.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98845
Approved by: https://github.com/ezyang
