net/hns3: fix mailbox opcode data type

net/hns3: fix mailbox opcode data type

The mailbox opcode is defined as one byte in datasheet which is not
compatible with that in the current hns3 PMD driver.

This patch fixes the data type of the local variable for mailbox opcode
in driver, changing from uint16_t to uint8_t.

Fixes: 463e748964f5 ("net/hns3: support mailbox")
Cc: stable@dpdk.org
Signed-off-by: Min Hu (Connor) <humin29@huawei.com>
Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>
Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>