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/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp
index 58d9050..186ef57 100644
--- a/llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -2642,7 +2642,7 @@
 unsigned RAGreedy::selectOrSplit(LiveInterval &VirtReg,
                                  SmallVectorImpl<unsigned> &NewVRegs) {
   CutOffInfo = CO_None;
-  LLVMContext &Ctx = MF->getFunction()->getContext();
+  LLVMContext &Ctx = MF->getFunction().getContext();
   SmallVirtRegSet FixedRegisters;
   unsigned Reg = selectOrSplitImpl(VirtReg, NewVRegs, FixedRegisters);
   if (Reg == ~0U && (CutOffInfo != CO_None)) {