MachineFunction: Return reference for getFrameInfo(); NFC

getFrameInfo() never returns nullptr so we should use a reference
instead of a pointer.

llvm-svn: 277017
diff --git a/llvm/lib/Target/ARM/ARMFastISel.cpp b/llvm/lib/Target/ARM/ARMFastISel.cpp
index 13724da..165a8be 100644
--- a/llvm/lib/Target/ARM/ARMFastISel.cpp
+++ b/llvm/lib/Target/ARM/ARMFastISel.cpp
@@ -2481,8 +2481,8 @@
   switch (I.getIntrinsicID()) {
   default: return false;
   case Intrinsic::frameaddress: {
-    MachineFrameInfo *MFI = FuncInfo.MF->getFrameInfo();
-    MFI->setFrameAddressIsTaken(true);
+    MachineFrameInfo &MFI = FuncInfo.MF->getFrameInfo();
+    MFI.setFrameAddressIsTaken(true);
 
     unsigned LdrOpc = isThumb2 ? ARM::t2LDRi12 : ARM::LDRi12;
     const TargetRegisterClass *RC = isThumb2 ? &ARM::tGPRRegClass