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 22b1b4448570a1ace42a0de35fbbae45ac0cef2f..16dd73e7f86b58e35eb0c85862eead541e4de540 100644
--- a/test/unittests/compiler/register-allocator-unittest.cc
+++ b/test/unittests/compiler/register-allocator-unittest.cc
@@ -320,11 +320,11 @@ TEST_F(RegisterAllocatorTest, SpillPhi) {
   EndBlock(Branch(Imm(), 1, 2));
 
   StartBlock();
-  auto left = Define(Reg(0));
+  auto left = Define(Reg(GetAllocatableCode(0)));

[ivica.bogosavljevic, 2016/10/19 14:30:40]

I guess the same thing should be done everywhere. That's why I wanted to add
this code to the definition of InstructionSequenceTest::Reg, but that method is
static so it wasn't possible. 

   EndBlock(Jump(2));
 
   StartBlock();
-  auto right = Define(Reg(0));
+  auto right = Define(Reg(GetAllocatableCode(0)));
   EndBlock();
 
   StartBlock();