Check for osmo_fsm_register() error return value

Change-Id: Idda1a4050cf9d285225ae48a4ba6f48c04f9598b
diff --git a/src/rspro_client_fsm.c b/src/rspro_client_fsm.c
index 45cd08e..c01a763 100644
--- a/src/rspro_client_fsm.c
+++ b/src/rspro_client_fsm.c
@@ -382,5 +382,5 @@
 
 static __attribute__((constructor)) void on_dso_load(void)
 {
-	osmo_fsm_register(&rspro_client_server_fsm);
+	OSMO_ASSERT(osmo_fsm_register(&rspro_client_server_fsm) == 0);
 }