MIPS64: Fix test Cvt_s_uw_Trunc_uw_s.

test/cctest/test-macro-assembler-mips64.cc

Index: test/cctest/test-macro-assembler-mips64.cc
diff --git a/test/cctest/test-macro-assembler-mips64.cc b/test/cctest/test-macro-assembler-mips64.cc
index 873da5cd17d221ce4792db733511c4a381eb53cc..b0aa76614e8bb701557a806e37379023f4701474 100644
--- a/test/cctest/test-macro-assembler-mips64.cc
+++ b/test/cctest/test-macro-assembler-mips64.cc
@@ -604,6 +604,7 @@ TEST(Cvt_s_uw_Trunc_uw_s) {
     CHECK_EQ(static_cast<float>(input),
              run_Cvt<uint64_t>(input, [](MacroAssembler* masm) {
                __ Cvt_s_uw(f0, a0);
+               __ mthc1(zero_reg, f2);
                __ Trunc_uw_s(f2, f0, f1);
              }));
   }