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/Mips/MipsTargetMachine.cpp b/llvm/lib/Target/Mips/MipsTargetMachine.cpp
index 9a12b98..85193bf 100644
--- a/llvm/lib/Target/Mips/MipsTargetMachine.cpp
+++ b/llvm/lib/Target/Mips/MipsTargetMachine.cpp
@@ -200,7 +200,7 @@
 void MipsTargetMachine::resetSubtarget(MachineFunction *MF) {
   DEBUG(dbgs() << "resetSubtarget\n");
 
-  Subtarget = const_cast<MipsSubtarget *>(getSubtargetImpl(*MF->getFunction()));
+  Subtarget = const_cast<MipsSubtarget *>(getSubtargetImpl(MF->getFunction()));
   MF->setSubtarget(Subtarget);
 }