e1000e: Correct NVM checksum verification flow

Update MAC type check e1000_pch_tgp because for e1000_pch_cnp,
NVM checksum update is still possible.
Emit a more detailed warning message.

Bugzilla: https://bugzilla.opensuse.org/show_bug.cgi?id=1191663
Fixes: 4051f683

 ("e1000e: Do not take care about recovery NVM checksum")
Reported-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>