i40e,igb,ixgbe: remove usless return statements

Remove cases where useless bare return is left at end of function.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>