Change default_impl in cpp backend to sp<>

Bug: 198787022
Test: atest aidl_test

Change-Id: I821693900a458d42f5cc6f1ad07429efc8bee983
diff --git a/tests/aidl_test_client_defaultimpl.cpp b/tests/aidl_test_client_defaultimpl.cpp
index c98aa4b..df57d2c 100644
--- a/tests/aidl_test_client_defaultimpl.cpp
+++ b/tests/aidl_test_client_defaultimpl.cpp
@@ -50,7 +50,7 @@
 }
 
 TEST_F(AidlTest, defaultImpl) {
-  std::unique_ptr<ITestService> defImpl = std::make_unique<Def>();
+  android::sp<ITestService> defImpl = android::sp<Def>::make();
   auto ret = ITestService::setDefaultImpl(std::move(defImpl));
   ASSERT_TRUE(ret);