Replace a few more "fall through" comments with LLVM_FALLTHROUGH

Follow up to r278902. I had missed "fall through", with a space.

llvm-svn: 278970
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
index 3c9cb17..709c2ce 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
@@ -362,7 +362,7 @@
       Result = Tmp1;
       break;
     }
-    // FALL THROUGH
+    LLVM_FALLTHROUGH;
   }
   case TargetLowering::Expand:
     Result = Expand(Op);