sched/bt: eliminate warning when booting with offline_class

offline_class was defined as an early_param. But the callback
function return 1 which lead to a warning message
"[    0.000000] Malformed early option 'offline_class'"
when booting.

Signed-off-by: Xiaoguang Chen <xiaoggchen@tencent.com>

init/main.c

@@ -359,7 +359,7 @@ static int __init set_sched_bt_on(char *str)
 {
     sched_bt_on = 1;
 
-    return 1;
+    return 0;
 }
 early_param("offline_class", set_sched_bt_on);