MachineFunction: Return reference from getFunction(); NFC

The Function can never be nullptr so we can return a reference.

llvm-svn: 320884
diff --git a/llvm/lib/Target/AArch64/AArch64ConditionOptimizer.cpp b/llvm/lib/Target/AArch64/AArch64ConditionOptimizer.cpp
index f765825..d14bde3 100644
--- a/llvm/lib/Target/AArch64/AArch64ConditionOptimizer.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ConditionOptimizer.cpp
@@ -327,7 +327,7 @@
 bool AArch64ConditionOptimizer::runOnMachineFunction(MachineFunction &MF) {
   DEBUG(dbgs() << "********** AArch64 Conditional Compares **********\n"
                << "********** Function: " << MF.getName() << '\n');
-  if (skipFunction(*MF.getFunction()))
+  if (skipFunction(MF.getFunction()))
     return false;
 
   TII = MF.getSubtarget().getInstrInfo();