[clang-rename] fix broken build

As Eric Fiselier pointed out, r278760 breaks build, because RecursiveASTVisitor
doesn't have a const overload. This patch is a quick fix.

llvm-svn: 278780
diff --git a/clang-tools-extra/clang-rename/USRFinder.cpp b/clang-tools-extra/clang-rename/USRFinder.cpp
index a554250..4007653 100644
--- a/clang-tools-extra/clang-rename/USRFinder.cpp
+++ b/clang-tools-extra/clang-rename/USRFinder.cpp
@@ -179,7 +179,7 @@
   NamedDeclFindingASTVisitor Visitor(Point, Context);
 
   // We only want to search the decls that exist in the same file as the point.
-  for (const auto *CurrDecl : Context.getTranslationUnitDecl()->decls()) {
+  for (auto *CurrDecl : Context.getTranslationUnitDecl()->decls()) {
     const SourceLocation FileLoc = CurrDecl->getLocStart();
     StringRef FileName = Context.getSourceManager().getFilename(FileLoc);
     // FIXME: Add test.