i40e: fix error return

If the VF asks to add an invalid MAC address, tell it that instead of
just using a generic return code.

Change-Id: I366aff5449fa5874ad51e2734cac2a71783ab14b
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>