[quant][graphmode][fx] Add warning for unsupported case

Summary:
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:

Reviewers:

Subscribers:

Tasks:

Tags:

ghstack-source-id: 3d3fe552470707374782ba89272d7d4473d1df13
Pull Request resolved: #45714

torch/quantization/fx/quantize.py

@@ -47,6 +47,7 @@
 )
 
 from collections import OrderedDict
+import warnings
 import copy
 import re
 
@@ -295,7 +296,13 @@ def get_qconfig(module_name):
             elif node.op == 'call_method':
                 self_obj = node.args[0]
                 # qconfig for call_method should be the same as the `self` object for the call
-                self.qconfig_map[node.name] = self.qconfig_map[self_obj.name]
+                if self_obj.name in self.qconfig_map:
+                    qconfig = self.qconfig_map[self_obj.name]
+                else:
+                    # need scope info for each node to support this
+                    warnings.warn("Scope info is not yet supported, taking default qconfig for value {}".format(node.name))
+                    qconfig = get_qconfig('')
+                self.qconfig_map[node.name] = qconfig
             elif node.op == 'call_module':
                 module_qconfig = get_qconfig(node.target)
                 # regex is not supported eager mode propagate_qconfig_, we'll need to