i40evf: don't give up

When the VF driver is unable to communicate with the PF, it just gives
up and never tries again. Aside from the obvious character flaw that
this shows, it's also a lousy user experience.

When PF communications fail, wait five seconds, and try again. And
again. Don't give up, little VF driver! Your prince will come!

Change-ID: Ia1378a39879883563b8faffce819f375821f9585
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>