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/ARMExpandPseudoInsts.cpp b/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp
index f1def98..b14b2c6 100644
--- a/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp
+++ b/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp
@@ -1259,7 +1259,7 @@
         MachineConstantPool *MCP = MF->getConstantPool();
         unsigned PCLabelID = AFI->createPICLabelUId();
         MachineConstantPoolValue *CPV =
-            ARMConstantPoolSymbol::Create(MF->getFunction()->getContext(),
+            ARMConstantPoolSymbol::Create(MF->getFunction().getContext(),
                                           "__aeabi_read_tp", PCLabelID, 0);
         unsigned Reg = MI.getOperand(0).getReg();
         MIB = BuildMI(MBB, MBBI, MI.getDebugLoc(),