net: hns3: replace magic value by HCLGE_RING_REG_OFFSET

Magic values are not recommended.

Signed-off-by: Peng <Li&lt;lipeng321@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>