net/hns3: remove unused assignment for RSS key

net/hns3: remove unused assignment for RSS key

The default RSS key does not need to be configured repeatedly
when call hns3_dev_configure function with the NULL RSS key
because the default RSS key has been configured when the PMD
driver run hns3_do_start function with starting device.

Besides, it will not overwrite the initialized key if
rte_eth_dev_configure API will be called directly and RSS key is NULL
after init PMD driver.

Therefore, the assignment for RSS key in hns3_dev_configure
function is unnecessary.

Signed-off-by: Lijun Ou <oulijun@huawei.com>