Subdivision iteration primvar not inherited on instances

[cpichard]

Describe the bug
When we set the attribute primvars:arnold:subdiv_iterations on a prim, the children inherit this primvar and set the subdiv on the meshes. In Arnold it will only work if the scene in parts of the scene that are not instanced but not on the instanced one.

To Reproduce
Steps to reproduce the behavior:

1. Using the pixar kitchen set non instanced, add the attribute at the root prim with a value of 5 for example
2. render with arnold - we can see the subdivision
3. Using the pixar kitchen set instanced, add the attribute at the root prim with a value of 5 for example
4. we can't see the subdivision.

[autodesk-oss-arnold-bot]

Issue synced internally to ARNOLD-15463