i40e: let go of the past

If we reset a VF, its VSI goes away, and it gets a new one. So don't
hang on to the now-stale local VSI pointer. It just leads to suffering
and kernel panics.

Change-ID: Ia8823b4e85893e95e963acee284968022b29177a
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>