[llvm] [NFC][SPIRV] Fix function type recovery (PR #165934)

[Nathan Gauër via llvm-commits]

================
@@ -153,19 +153,21 @@ static FunctionType *getOriginalFunctionType(const Function &F) {
   // so we should support this.
----------------
Keenuts wrote:

Is this TODO still up to date now?

https://github.com/llvm/llvm-project/pull/165934