i40e: Code cleanup in i40e_add_fdir_ethtool

A little bit of code cleanup in prep for more cloud filter work.

Change-ID: I0dc33ce0d4c207944336a07437640fef920c100c
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>