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/ARM/ARMFastISel.cpp b/llvm/lib/Target/ARM/ARMFastISel.cpp
index 1090f62..0ea4350 100644
--- a/llvm/lib/Target/ARM/ARMFastISel.cpp
+++ b/llvm/lib/Target/ARM/ARMFastISel.cpp
@@ -2958,7 +2958,7 @@
                                      unsigned Align, MVT VT) {
   bool UseGOT_PREL = !TM.shouldAssumeDSOLocal(*GV->getParent(), GV);
 
-  LLVMContext *Context = &MF->getFunction()->getContext();
+  LLVMContext *Context = &MF->getFunction().getContext();
   unsigned ARMPCLabelIndex = AFI->createPICLabelUId();
   unsigned PCAdj = Subtarget->isThumb() ? 4 : 8;
   ARMConstantPoolValue *CPV = ARMConstantPoolConstant::Create(