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/FEntryInserter.cpp b/llvm/lib/CodeGen/FEntryInserter.cpp
index dbe6b30..4ddf9f9 100644
--- a/llvm/lib/CodeGen/FEntryInserter.cpp
+++ b/llvm/lib/CodeGen/FEntryInserter.cpp
@@ -36,7 +36,7 @@
 
 bool FEntryInserter::runOnMachineFunction(MachineFunction &MF) {
   const std::string FEntryName =
-      MF.getFunction()->getFnAttribute("fentry-call").getValueAsString();
+      MF.getFunction().getFnAttribute("fentry-call").getValueAsString();
   if (FEntryName != "true")
     return false;