i40e: avoid unnecessary register read

We don't need to read the base VF id. It's already stashed in the HW
struct.

Change-Id: Ib81e2f76fc40b12c966e014a856b481912cafefc
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>