MachineFunction: Return reference from getFunction(); NFC

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320884 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/PPCMIPeephole.cpp b/lib/Target/PowerPC/PPCMIPeephole.cpp
index 64c5e4e..27ded63 100644
--- a/lib/Target/PowerPC/PPCMIPeephole.cpp
+++ b/lib/Target/PowerPC/PPCMIPeephole.cpp
@@ -106,7 +106,7 @@
 
   // Main entry point for this pass.
   bool runOnMachineFunction(MachineFunction &MF) override {
-    if (skipFunction(*MF.getFunction()))
+    if (skipFunction(MF.getFunction()))
       return false;
     initialize(MF);
     return simplifyCode();