[pattern rewriter] Dont return value from void function

R=adamk@chromium.org

Review-Url: https://codereview.chromium.org/2626493002
Cr-Commit-Position: refs/heads/master@{#42156}

src/parsing/pattern-rewriter.cc

@@ -309,7 +309,7 @@ void Parser::PatternRewriter::VisitRewritableExpression(
     block_->statements()->Add(factory()->NewExpressionStatement(expr, pos),
                               zone());
   }
-  return set_context(old_context);
+  set_context(old_context);
 }
 
 // When an extra declaration scope needs to be inserted to account for