igc: Remove forced_speed_duplex value

u8 forced_speed_duplex from value from igc_mac_info struct is not used.
This patch comes to tidy up the driver code.

Signed-off-by: Sasha Neftin <[e-mail]>
Signed-off-by: Tony Nguyen <[e-mail]>

drivers/net/ethernet/intel/igc/igc_hw.h

···
 	u32 mta_shadow[MAX_MTA_REG];
 	u16 rar_entry_count;
 
-	u8 forced_speed_duplex;
-
 	bool asf_firmware_present;
 	bool arc_subsystem_valid;