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/Target/ARM/ARMFastISel.cpp b/llvm/lib/Target/ARM/ARMFastISel.cpp
index 960b711..9b4747b 100644
--- a/llvm/lib/Target/ARM/ARMFastISel.cpp
+++ b/llvm/lib/Target/ARM/ARMFastISel.cpp
@@ -1868,6 +1868,7 @@
       return (Return ? RetCC_ARM_AAPCS_VFP: CC_ARM_AAPCS_VFP);
     // Fall through to soft float variant, variadic functions don't
     // use hard floating point ABI.
+    LLVM_FALLTHROUGH;
   case CallingConv::ARM_AAPCS:
     return (Return ? RetCC_ARM_AAPCS: CC_ARM_AAPCS);
   case CallingConv::ARM_APCS: