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

Since nldev_deldev() (introduced by commit 060c642b2ab8 ("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: [e-mail]
Closes: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
Fixes: bca51197620a ("RDMA/core: Support IB sub device with type "SMI"")
Signed-off-by: Tetsuo Handa <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Reviewed-by: Parav Pandit <[e-mail]>
Signed-off-by: Leon Romanovsky <[e-mail]>

drivers/infiniband/core/device.c

···
 {
 	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);