[RegAllocGreedy] Remove unnecessary conversion from MCRegister to Register. NFC

Author: topperc

llvm/lib/CodeGen/RegAllocGreedy.cpp

@@ -2456,7 +2456,7 @@ MCRegister RAGreedy::selectOrSplitImpl(const LiveInterval &VirtReg,
   // queue. The RS_Split ranges already failed to do this, and they should not
   // get a second chance until they have been split.
   if (Stage != RS_Split)
-    if (Register PhysReg =
+    if (MCRegister PhysReg =
             tryEvict(VirtReg, Order, NewVRegs, CostPerUseLimit,
                      FixedRegisters)) {
       Register Hint = MRI->getSimpleHint(VirtReg.reg());