i40e: Update i40e_init_dcb to return correct error

Modify the i40e_init_dcb to return the correct error when LLDP or DCBX
is not in operational state.

Signed-off-by: Chinh T Cao <chinh.t.cao@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>