MCContext.cpp: Fixup for my odd previous commit. No functional changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159645 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCContext.cpp b/lib/MC/MCContext.cpp
index b535b3e..b5b14b9 100644
--- a/lib/MC/MCContext.cpp
+++ b/lib/MC/MCContext.cpp
@@ -278,7 +278,7 @@
     if (!tFileName.empty()) {
       Directory = sys::path::parent_path(FileName);
       if (!Directory.empty())
-        FileName = sys::path::filename(FileName);
+        FileName = tFileName;
     }
   }