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/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 2dab5b6..6424e08 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1983,8 +1983,8 @@
             MemIntrinsic *MI = cast<MemIntrinsic>(II);
             if (MI->isVolatile() || MI->getRawDest() != PI)
               return false;
+            LLVM_FALLTHROUGH;
           }
-          // fall through
           case Intrinsic::dbg_declare:
           case Intrinsic::dbg_value:
           case Intrinsic::invariant_start: