RDMA/core: always drop device refcount in ib_del_sub_device_and_put()

Since nldev_deldev() (introduced by commit 060c642 ("RDMA/nldev: Add
support to add/delete a sub IB device through netlink") grabs a reference
using ib_device_get_by_index() before calling ib_del_sub_device_and_put(),
we need to drop that reference before returning -EOPNOTSUPP error.

Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
Fixes: bca5119 ("RDMA/core: Support IB sub device with type "SMI"")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: https://patch.msgid.link/80749a85-cbe2-460c-8451-42516013f9fa@I-love.SAKURA.ne.jp
Reviewed-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>

Author: Tetsuo Handa

drivers/infiniband/core/device.c

@@ -2881,8 +2881,10 @@ int ib_del_sub_device_and_put(struct ib_device *sub)
 {
 	struct ib_device *parent = sub->parent;
 
-	if (!parent)
+	if (!parent) {
+		ib_device_put(sub);
 		return -EOPNOTSUPP;
+	}
 
 	mutex_lock(&parent->subdev_lock);
 	list_del(&sub->subdev_list);