net: hns: fix device reference leaks

Make sure to drop the reference taken by class_find_device() in
hnae_get_handle() on errors and when later releasing the handle.

Fixes: 6fe6611f

 ("net: add Hisilicon Network Subsystem...")
Cc: Yisen Zhuang <yisen.zhuang@huawei.com>
Cc: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>