MC/AsmLexer: Fix bug in source location for Slash token.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117298 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCParser/AsmLexer.cpp b/lib/MC/MCParser/AsmLexer.cpp
index 7ca1ccc..867cb20 100644
--- a/lib/MC/MCParser/AsmLexer.cpp
+++ b/lib/MC/MCParser/AsmLexer.cpp
@@ -119,7 +119,7 @@
   switch (*CurPtr) {
   case '*': break; // C style comment.
   case '/': return ++CurPtr, LexLineComment();
-  default:  return AsmToken(AsmToken::Slash, StringRef(CurPtr, 1));
+  default:  return AsmToken(AsmToken::Slash, StringRef(CurPtr-1, 1));
   }
 
   // C Style comment.