e1000e: disregard NVM checksum on tgp when valid checksum bit is not set

As described by Vitaly Lifshits:

> Starting from Tiger Lake, LAN NVM is locked for writes by SW, so the
> driver cannot perform checksum validation and correction. This means
> that all NVM images must leave the factory with correct checksum and
> checksum valid bit set. Since Tiger Lake devices were the first to have
> this lock, some systems in the field did not meet this requirement.
> Therefore, for these transitional devices we skip checksum update and
> verification, if the valid bit is not set.

Signed-off-by: Jacek Kowalski <jacek@jacekk.info>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Vitaly Lifshits <vitaly.lifshits@intel.com>
Fixes: 4051f68 ("e1000e: Do not take care about recovery NVM checksum")
Cc: stable@vger.kernel.org
Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

Author: jacekkow

drivers/net/ethernet/intel/e1000e/ich8lan.c

@@ -4274,6 +4274,8 @@ static s32 e1000_validate_nvm_checksum_ich8lan(struct e1000_hw *hw)
 			ret_val = e1000e_update_nvm_checksum(hw);
 			if (ret_val)
 				return ret_val;
+		} else if (hw->mac.type == e1000_pch_tgp) {
+			return 0;
 		}
 	}