igb/ixgbe: remove return statements for void functions

Remove useless return statements for void functions which do not need
it.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>

diff --cc drivers/net/ethernet/intel/igb/e1000_nvm.c
Simple merge

diff --cc drivers/net/ethernet/intel/ixgbe/ixgbe_82598.c
Simple merge

diff --cc drivers/net/ethernet/intel/ixgbe/ixgbe_dcb.c
Simple merge