MIPS: Fix bad RegisterConfiguration usage in InstructionSequence unit tests.

test/unittests/compiler/register-allocator-unittest.cc

Index: test/unittests/compiler/register-allocator-unittest.cc
diff --git a/test/unittests/compiler/register-allocator-unittest.cc b/test/unittests/compiler/register-allocator-unittest.cc
index ed3558dc609606daaf366e83e02cbb704147a6ec..0533ee74069af3c783ee66e81f6d7b893381b30a 100644
--- a/test/unittests/compiler/register-allocator-unittest.cc
+++ b/test/unittests/compiler/register-allocator-unittest.cc
@@ -321,11 +321,11 @@ TEST_F(RegisterAllocatorTest, SpillPhi) {
   EndBlock(Branch(Imm(), 1, 2));
 
   StartBlock();
-  auto left = Define(Reg(0));
+  auto left = Define(Reg(GetAllocatableCode(0)));
   EndBlock(Jump(2));
 
   StartBlock();
-  auto right = Define(Reg(0));
+  auto right = Define(Reg(GetAllocatableCode(0)));
   EndBlock();
 
   StartBlock();