net: sched: remove the unused return value of unregister_qdisc

Return value of unregister_qdisc is unused, remove it.

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Link: https://lore.kernel.org/r/20220815030417.271894-1-shaozhengchao@huawei.com


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