[MAYA-121075] Material connections break on skinned objects with more than one material

**Describe the bug**
If a mesh is skinned **and** has more that one material applied to a single mesh node, the material will break if a USD is imported and saved as a Maya Scene.

**Steps to reproduce**
Steps to reproduce the behavior:
1. Open the attached scene "multi_material.mb"
2. Observe one sphere has 1 material and the other one has 2 materials
3. File > Export All, set subd to None and include UsdSkel, choose a file name
4. File > New
5. File > Import, choose the file you exported
6. Notice it looks correct
7. File > Save, choose a Maya file name
8. File > Open, pick the Maya file you just saved
9. Notice the neon green sphere, indicated that the material connections are broken

**Expected behavior**
Material should not be broken

**Attachments**

[material_import_bug.zip](https://github.com/Autodesk/maya-usd/files/8732124/material_import_bug.zip)

Inside the attachment are the resulting usd file I got and my scene after the import and save.

**Specs (if applicable):**
- Windows 10 pro
- Maya PR134

**Additional context**
Add any other context about the problem here.