net: hns3: Fixes the command used to unmap ring from vector

This patch fixes the IMP command being used to unmap the vector
from the corresponding ring.

Fixes: 6427264ef330 ("net: hns3: Add HNS3 Acceleration Engine &
Compatibility Layer Support")
Signed-off-by: Lipeng <lipeng321@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>