bdi: fix memleak in bdi_register_va()

hulk inclusion
category: bugfix
bugzilla: 30109
CVE: NA
---------------------------

When device_add() fail, we just free rcu_dev and
forget kobj->name. Using put_devcie to free both
of rcu_dev and kobj->name.

Fixes: 5ca4579ae59b ("bdi: fix use-after-free for the bdi device")
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>