net: hns: remove useless variable assignment and comment

The variable head in hns_nic_tx_fini_pro has read a value, but it is
obviously no use. The patch will fix it.
And the comment is nothing to do with the routine, so it has to be removed

Signed-off-by: Qianqian Xie <xieqianqian@huawei.com>
Signed-off-by: Yisen Zhuang <Yisen.Zhuang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>