[OpenMP] [Semantics] [Flang] Fix build error caused by unused variable.

[raghavendhra]

Summary

Fixed build error caused by unused variable 'dataRef' in https://reviews.llvm.org/D155133

[vdonaldson]

@raghavendhra Thanks for the fix!

flang/lib/Semantics/check-omp-structure.cpp

 
 void OmpStructureChecker::CheckStructureElement(
     const parser::OmpObjectList &ompObjectList,
     const llvm::omp::Clause clause) {
   for (const auto &ompObject : ompObjectList.v) {
     common::visit(
         common::visitors{
             [&](const parser::Designator &designator) {
-              if (const auto *dataRef{
-                      std::get_if<parser::DataRef>(&designator.u)}) {
+              if (std::get_if<parser::DataRef>(&designator.u)) {
                 if (parser::Unwrap<parser::StructureComponent>(ompObject)) {
                   context_.Say(GetContext().clauseSource,
                       "A variable that is part of another variable "
                       "(structure element) cannot appear on the %s "
                       "%s clause"_err_en_US,
                       ContextDirectiveAsFortran(),
                       parser::ToUpperCaseLetters(getClauseName(clause).str()));
                 }