net_sched: hfsc: Fix a potential UAF in hfsc_dequeue() too

[ Upstream commit 6ccbda44e2cc3d26fd22af54c650d6d5d801addf ]

Similarly to the previous patch, we need to safe guard hfsc_dequeue()
too. But for this one, we don't have a reliable reproducer.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Reported-by: Gerrard Tai <gerrard.tai@starlabs.sg>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20250417184732.943057-3-xiyou.wangcong@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>