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/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index cc61fc7..341692f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -457,9 +457,9 @@
                                          V1->getName()+".mask");
           return BinaryOperator::Create(Op0BO->getOpcode(), YS, XM);
         }
+        LLVM_FALLTHROUGH;
       }
 
-      // FALL THROUGH.
       case Instruction::Sub: {
         // Turn ((X >> C) + Y) << C  ->  (X + (Y << C)) & (~0 << C)
         if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&