debugobjects: Recheck debug_objects_enabled before reporting

syzbot is reporting false a positive ODEBUG message immediately after
ODEBUG was disabled due to OOM.

  [ 1062.309646][T22911] ODEBUG: Out of memory. ODEBUG disabled
  [ 1062.886755][ T5171] ------------[ cut here ]------------
  [ 1062.892770][ T5171] ODEBUG: assert_init not available (active state 0) object: ffffc900056afb20 object type: timer_list hint: process_timeout+0x0/0x40

  CPU 0 [ T5171]                CPU 1 [T22911]
  --------------                --------------
  debug_object_assert_init() {
    if (!debug_objects_enabled)
      return;
    db = get_bucket(addr);
                                lookup_object_or_alloc() {
                                  debug_objects_enabled = 0;
                                  return NULL;
                                }
                                debug_objects_oom() {
                                  pr_warn("Out of memory. ODEBUG disabled\n");
                                  // all buckets get emptied here, and
                                }
    lookup_object_or_alloc(addr, db, descr, false, true) {
      // this bucket is already empty.
      return ERR_PTR(-ENOENT);
    }
    // Emits false positive warning.
    debug_print_object(&o, "assert_init");
  }

Recheck debug_object_enabled in debug_print_object() to avoid that.

Reported-by: syzbot <syzbot+7937ba6a50bdd00fffdf@syzkaller.appspotmail.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/492fe2ae-5141-d548-ebd5-62f5fe2e57f7@I-love.SAKURA.ne.jp
Closes: https://syzkaller.appspot.com/bug?extid=7937ba6a50bdd00fffdf