tty: Move the leader test in disassociate

There are two call points, both want to check that tty->signal->leader is
set. Move the test into disassociate_ctty() as that will make locking
changes easier in a bit

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

kernel/exit.c

@@ -971,7 +971,7 @@ NORET_TYPE void do_exit(long code)
 	exit_thread();
 	cgroup_exit(tsk, 1);
 
-	if (group_dead && tsk->signal->leader)
+	if (group_dead)
 		disassociate_ctty(1);
 
 	module_put(task_thread_info(tsk)->exec_domain->module);