Fix T48732, OpenCL compile failure after Multiscatter GGX commit.
Fix T48732, OpenCL compile failure after Multiscatter GGX commit.

Use OpenCL "all" builtin type for conversion, according to OpenCL 1.1 spec 6.3e.

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