net: ethtool: remove error check for legacy setting transceiver type

Commit 9cab88726929605 ("net: ethtool: Add back transceiver type")
restores the transceiver type to struct ethtool_link_settings and
convert_link_ksettings_to_legacy_settings() but forgets to remove the
error check for the same in convert_legacy_settings_to_link_ksettings().
This prevents older versions of ethtool to change link settings.

    # ethtool --version
    ethtool version 3.16

    # ethtool -s eth0 autoneg on speed 100 duplex full
    Cannot set new settings: Invalid argument
      not setting speed
      not setting duplex
      not setting autoneg

While newer versions of ethtool works.

    # ethtool --version
    ethtool version 4.10

    # ethtool -s eth0 autoneg on speed 100 duplex full
    [   57.703268] sh-eth ee700000.ethernet eth0: Link is Down
    [   59.618227] sh-eth ee700000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx

Fixes: 19cab887 ("net: ethtool: Add back transceiver type")
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reported-by: Renjith R V <renjith.rv@quest-global.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>