spirv: Fix SpvOpExpectKHR
What does this MR do and why?
spirv: Fix SpvOpExpectKHR
This instruction behaves the same as *OpCopyObject* by making a copy of _Value_.
Fixes: 25bc3d2824b8f27fd23e5ade8f7b9509174b423d ('spirv/nir_to_spirv: add expect assume op codes')