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/X86/X86SelectionDAGInfo.cpp b/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
index d006556..1e04997 100644
--- a/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
+++ b/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
@@ -247,7 +247,7 @@
       Repeats.AVT = Subtarget.is64Bit() ? MVT::i64 : MVT::i32;
 
     if (Repeats.BytesLeft() > 0 &&
-        DAG.getMachineFunction().getFunction()->optForMinSize()) {
+        DAG.getMachineFunction().getFunction().optForMinSize()) {
       // When agressively optimizing for size, avoid generating the code to
       // handle BytesLeft.
       Repeats.AVT = MVT::i8;