igc: remove autoneg parameter from igc_mac_info

Since the igc driver doesn't support forced speed configuration and
its current related hardware doesn't support it either, there is no
use of the mac.autoneg parameter. Moreover, in one case this usage
might result in a NULL pointer dereference due to an uninitialized
function pointer, phy.ops.force_speed_duplex.

Therefore, remove this parameter from the igc code.

Signed-off-by: Vitaly Lifshits <vitaly.lifshits@intel.com>
Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>