Check for osmo_fsm_register() error return value

Change-Id: Idbc1557739b2a253b73914e6f1f18a6d169d882e
diff --git a/tests/use_count/use_count_test.c b/tests/use_count/use_count_test.c
index 0b081c9..95af308 100644
--- a/tests/use_count/use_count_test.c
+++ b/tests/use_count/use_count_test.c
@@ -331,7 +331,7 @@
 	log_set_print_level(osmo_stderr_target, 1);
 	log_set_use_color(osmo_stderr_target, 0);
 
-	osmo_fsm_register(&foo_fsm);
+	OSMO_ASSERT(osmo_fsm_register(&foo_fsm) == 0);
 
 	test_use_count_fsm();