net: hns3: make symbol 'hclge_mac_speed_map_to_fw' static

The sparse tool complains as follows:

drivers/net/ethernet/hisilicon/hns3/hns3pf/hclge_main.c:2656:28: warning:
 symbol 'hclge_mac_speed_map_to_fw' was not declared. Should it be static?

This symbol is not used outside of hclge_main.c, so marks it static.

Fixes: e46da6a3 ("net: hns3: refine function hclge_cfg_mac_speed_dup_hw()")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>