[NFC] Update SemaRef.Diag to just Diag in OpenACC implementation

I missed these two in my last patch as the two patches crossed in
review, so correct this now.

Author: erichkeane

clang/lib/Sema/SemaOpenACC.cpp

@@ -102,10 +102,10 @@ SemaOpenACC::ActOnClause(ArrayRef<const OpenACCClause *> ExistingClauses,
     });
 
     if (Itr != ExistingClauses.end()) {
-      SemaRef.Diag(Clause.getBeginLoc(),
+      Diag(Clause.getBeginLoc(),
                    diag::err_acc_duplicate_clause_disallowed)
           << Clause.getDirectiveKind() << Clause.getClauseKind();
-      SemaRef.Diag((*Itr)->getBeginLoc(), diag::note_acc_previous_clause_here);
+      Diag((*Itr)->getBeginLoc(), diag::note_acc_previous_clause_here);
       return nullptr;
     }