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/MachineScheduler.cpp b/llvm/lib/CodeGen/MachineScheduler.cpp
index 6be1373..e15eb65 100644
--- a/llvm/lib/CodeGen/MachineScheduler.cpp
+++ b/llvm/lib/CodeGen/MachineScheduler.cpp
@@ -351,7 +351,7 @@
 /// design would be to split blocks at scheduling boundaries, but LLVM has a
 /// general bias against block splitting purely for implementation simplicity.
 bool MachineScheduler::runOnMachineFunction(MachineFunction &mf) {
-  if (skipFunction(*mf.getFunction()))
+  if (skipFunction(mf.getFunction()))
     return false;
 
   if (EnableMachineSched.getNumOccurrences()) {
@@ -389,7 +389,7 @@
 }
 
 bool PostMachineScheduler::runOnMachineFunction(MachineFunction &mf) {
-  if (skipFunction(*mf.getFunction()))
+  if (skipFunction(mf.getFunction()))
     return false;
 
   if (EnablePostRAMachineSched.getNumOccurrences()) {