PCI: Remove VFs in reverse order if virtfn_add() fails

If virtfn_add() fails, we call virtfn_remove() for any previously added
devices.  Remove the devices in reverse order (first-added is
last-removed), which is more natural and doesn't require an additional
variable.

[bhelgaas: changelog, split to separate patch for reviewability]
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Wei Yang <weiyang@linux.vnet.ibm.com>