[quant][graphmode][fx] Add warning for unsupported case (#45714)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45714
Hit the problem when writing a test like following:
```
class M(...):
def forward(self, x):
x = x.some_op()
return x
```
we need to know the scope of `x` to figure out the qconfig for `x`
Test Plan: Imported from OSS
Reviewed By: z-a-f
Differential Revision: D24069959
fbshipit-source-id: 95ac8963c802ebce5d0e54d55f5ebb42085ca8a6
