mips msa vpx subtract test added

Change-Id: I0f0827a665c4d3039d3e5f09fa8c75c8f2bb2bab

test/vp9_subtract_test.cc

diff --git a/test/vp9_subtract_test.cc b/test/vp9_subtract_test.cc
index d78b277..3cad4d7 100644
--- a/test/vp9_subtract_test.cc
+++ b/test/vp9_subtract_test.cc
@@ -101,5 +101,9 @@
 INSTANTIATE_TEST_CASE_P(NEON, VP9SubtractBlockTest,
                         ::testing::Values(vpx_subtract_block_neon));
 #endif
+#if HAVE_MSA
+INSTANTIATE_TEST_CASE_P(MSA, VP9SubtractBlockTest,
+                        ::testing::Values(vpx_subtract_block_msa));
+#endif
 
 }  // namespace vp9