Fix T74393: Cycles crashes when both OSL and Optix Denoising are enabled
Fix T74393: Cycles crashes when both OSL and Optix Denoising are enabled

Enabling viewport denoising causes Cycles to use a multi-device, which always returned NULL when
asked for OSL memory and would subsequently crash. This fixes that by returning the correct OSL
memory pointer from the CPU device in the special viewport denoising multi-device.

tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird