[flang] [llvm] [flang][OpenMP] Avoid early returns, NFC (PR #117231)

[Steve Scalpone via llvm-commits]

sscalpone wrote:

I'm having trouble building with this change.   Same as llvm-ci above.   GCC 9.3.

```
In file included from /local/home/sscalpone/lorado/src/llvm-project/flang/lib/Lower/OpenMP/ClauseProcessor.cpp:13:
In file included from /local/home/sscalpone/lorado/src/llvm-project/flang/lib/Lower/OpenMP/ClauseProcessor.h:15:
/local/home/sscalpone/lorado/src/llvm-project/flang/lib/Lower/OpenMP/Clauses.h:169:25: error: template parameter redefines default argument
  169 |     typename ResultTy = std::invoke_result_t<FuncTy, typename ArgTy::Value>>
      |                         ^
/local/home/sscalpone/lorado/src/llvm-project/flang/lib/Lower/OpenMP/Clauses.h:159:25: note: previous default template argument defined here
  159 |     typename ResultTy = std::invoke_result_t<FuncTy, typename ArgTy::Value>>
      |                         ^
/local/home/sscalpone/lorado/src/llvm-project/flang/lib/Lower/OpenMP/Clauses.h:170:25: error: redefinition of 'maybeApplyToV'
  170 | std::optional<ResultTy> maybeApplyToV(FuncTy &&func, const ArgTy *arg) {
      |                         ^
/local/home/sscalpone/lorado/src/llvm-project/flang/lib/Lower/OpenMP/Clauses.h:160:25: note: previous definition is here
  160 | std::optional<ResultTy> maybeApplyToV(FuncTy &&func, const ArgTy *arg) {
      |                         ^
2 errors generated.
```

https://github.com/llvm/llvm-project/pull/117231