i40e: check pointers before use

Make sure we don't try to dereference NULL pointers when returning values
from the AdminQ calls.

Change-ID: Ia6694f2f415d50acf0aba063c863568742799aff
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>