sercomm_test.c: return correctly in main

Change-Id: I57fd3e1bf74ec24dec692710359a1ce00ecde75a
diff --git a/tests/sercomm/sercomm_test.c b/tests/sercomm/sercomm_test.c
index 8b1ffdf..f4f1c22 100644
--- a/tests/sercomm/sercomm_test.c
+++ b/tests/sercomm/sercomm_test.c
@@ -133,4 +133,5 @@
 int main(int argc, char **argv)
 {
 	test_sercomm();
+	return 0;
 }