fsm: log calling file+line for error "event for NULL fi"

Change-Id: I1970773440865f1415004bcf0164603468acf90b
diff --git a/src/fsm.c b/src/fsm.c
index 8675f75..c9902ae 100644
--- a/src/fsm.c
+++ b/src/fsm.c
@@ -384,8 +384,9 @@
 	const struct osmo_fsm_state *fs;
 
 	if (!fi) {
-		LOGP(DLGLOBAL, LOGL_ERROR, "Trying to dispatch event %u to "
-		     "non-existing FSM Instance!\n", event);
+		LOGPSRC(DLGLOBAL, LOGL_ERROR, file, line,
+			"Trying to dispatch event %u to non-existent"
+			" FSM instance!\n", event);
 		osmo_log_backtrace(DLGLOBAL, LOGL_ERROR);
 		return -ENODEV;
 	}