hisilicon: Update drivers to use ethtool_sprintf

Update the hisilicon drivers to make use of ethtool_sprintf. The general
idea is to reduce code size and overhead by replacing the repeated pattern
of string printf statements and ETH_STRING_LEN counter increments.

Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>