i40e: remove BUG_ON from FCoE setup

There's no need to kill the kernel thread here. If this condition was
true, the probe() would have died long before we got here. In any case,
we'll get the same result when this code tries to use the VSI pointer
being checked.

Prompted by a recent Linus diatribe.

Change-ID: I62f531cac34d4fc28ff9657d5b2d9523ae5e33a4
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>