fx quant: fix warning in util function when cloning tensors (#80883)
Summary:
Some of the util functions in FX graph mode quantization throw warnings
such as:
```
/Users/vasiliy/pytorch/torch/ao/quantization/fx/utils.py:410: UserWarning: To copy construct from
a tensor, it is recommended to use sourceTensor.clone().detach() or sourceTensor.clone().detach().
requires_grad_(True), rather than torch.tensor(sourceTensor).
```
This PR fixes the warnings by moving the code to the recommended syntax if the
value is a tensor.
Test plan:
```
python test/test_quantization.py -k test_conv_linear_reference
// warning appeared before this PR and disappeared after this PR
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80883
Approved by: https://github.com/jerryzh168
