i40e: fix whitespace issues in i40e_ethtool.c

There's a number of minor incidental whitespace issues in this file.
This addresses most of the ones I could find.

Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>