tracing/filters: Fix to make system filter work

commit fce29d15
("tracing/filters: Refactor subsystem filter code")
broke system filter accidentally.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <4AE810BD.3070009@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_events_filter.c

@@ -1230,12 +1230,12 @@ static int replace_system_preds(struct event_subsystem *system,
 				struct filter_parse_state *ps,
 				char *filter_string)
 {
-	struct event_filter *filter = system->filter;
 	struct ftrace_event_call *call;
 	bool fail = true;
 	int err;
 
 	list_for_each_entry(call, &ftrace_events, list) {
+		struct event_filter *filter = call->filter;
 
 		if (!call->define_fields)
 			continue;