i40e: Fix firmware API version errors

Reword the error messages. Also add a major version check because
We only want to warn on nvm_minor > expected_minor if
nvm_major == expected_major. Lastly, change an if to an else if
because the two statements will never evaluate to true at the same time.

Change-ID: I6ddf9986f26b35f6879cbeac4fcef04a8497a383
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Jim Young <jamesx.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>