Per-face shaders do not render in Solaris viewport

**Describe the bug**
Per-face shaders do not render in Solaris viewport

**To Reproduce**
1. Set up per-face shaders in Maya
2. Export to usd, using either arnold-usd or maya-usd
3. Bring into Solaris and render

Repro scene:
[test_faces_001.ma.zip](https://github.com/Autodesk/arnold-usd/files/11057213/test_faces_001.ma.zip)

Start by opening the linked test_faces_001.ma.zip scene and reproduce the issue in Solaris after exporting through arnold-usd and maya-usd. Compare the exported per-face shader assignments with the Solaris render; done means the per-face shaders render correctly in the viewport and final render.

Written by the indexing model from the issue text.