tracing: fix event_subsystem ref counting

Fix a bug introduced by e9dbfae, which prevents event_subsystem from
ever being released.

Ref_count was added to keep track of subsystem users, not for counting
events.  Subsystem is created with ref_count = 1, so there is no need to
increment it for every event, we have nr_events for that.  Fix this by
touching ref_count only when we actually have a new user -
subsystem_open().

Cc: [email protected]
Signed-off-by: Ilya Dryomov <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Steven Rostedt <[email protected]>

kernel/trace/trace_events.c

@@ -1078,7 +1078,6 @@ event_subsystem_dir(const char *name, struct dentry *d_events)
 	/* First see if we did not already create this dir */
 	list_for_each_entry(system, &event_subsystems, list) {
 		if (strcmp(system->name, name) == 0) {
-			__get_system(system);
 			system->nr_events++;
 			return system->entry;
 		}