i40e: Remove unnecessary pf members

We can use the stat index macro directly, a variable is not required.

Change-ID: I19f08ac16353dc0cd87a1a8248d714e15a54aa8a
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>