net: hns3: Clear client pointer when initialize client failed or unintialize finished

If initialize client failed or finish uninitializing client, we should
clear the client pointer. It may cause unexpected result when use
uninitialized client. Meanwhile, we also should check whether client
exist when uninitialize it.

Fixes: 46a3df9f ("net: hns3: Add HNS3 Acceleration Engine & Compatibility Layer Support")
Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>