net: fjes: use ethtool string helpers

The latter is the preferred way to copy ethtool strings.

Avoids manually incrementing the pointer.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241029232721.8442-1-rosenp@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>