i40e: Force register writes to mitigate sync issues with iwarp VF driver

This patch is a fix for the bug i.e. unable to create iwarp device
in VF. This is a sync issue and the iwarp device open is called even
before the PCI register writes are done.

Forcing the PCI register writes to happen just before it exits the
function.

Change-ID: I60c6a2c709da89e845f2764cc50ce8b7373c8c44
Signed-off-by: Avinash Dayanand <avinash.dayanand@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>