[5.8] [substrate] OpenPbr Material Function is wrong

Summary

[Bug] OpenPBR opaque material function uses base_diffuse_roughness on dielectrics as the roughness on the substrate material. It should use the specular roughness instead, as substrate does not have a diffuse roughness at all, for now it would be best to discard base_diffuse_roughness and its properties from an openpbr shader

What Type of Bug are you experiencing?

Editor

Steps to Reproduce

Import an OpenPBR Material that makes use of specular roughness and is a dielectric.

Expected Result

the shader should look roughly the same.

Observed Result

Everything is glossy and highly reflective.

Affects Versions

5.8

Platform(s)

Windows

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