Add an empty test target.

Change-Id: Ic8537ec4d62f3da6c3b0ba03eaaf746e4e5151fa
diff --git a/rcu_audio/Makefile b/rcu_audio/Makefile
index 71ef498..aa98aba 100644
--- a/rcu_audio/Makefile
+++ b/rcu_audio/Makefile
@@ -32,3 +32,6 @@
 
 clean:
 	rm -f $(BINARIES) *.o
+
+test:
+	true