[PathV2] Fix bug in relative_path.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151675 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/PathV2.cpp b/lib/Support/PathV2.cpp
index 3ef13e2..bf8672b 100644
--- a/lib/Support/PathV2.cpp
+++ b/lib/Support/PathV2.cpp
@@ -346,7 +346,7 @@
 
 const StringRef relative_path(StringRef path) {
   StringRef root = root_path(path);
-  return root.substr(root.size());
+  return path.substr(root.size());
 }
 
 void append(SmallVectorImpl<char> &path, const Twine &a,