Fix another typo in the classof definitions that doesn't (currently)
have any effect. Spotted by Eli in review, thanks!!!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174121 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCAsmStreamer.cpp b/lib/MC/MCAsmStreamer.cpp
index 71be1a9..7eb7202 100644
--- a/lib/MC/MCAsmStreamer.cpp
+++ b/lib/MC/MCAsmStreamer.cpp
@@ -279,7 +279,7 @@
   /// @}
 
   static bool classof(const MCStreamer *S) {
-    return S->getKind() == SK_NullStreamer;
+    return S->getKind() == SK_AsmStreamer;
   }
 };