PCI: Refresh First VF Offset and VF Stride when updating NumVFs

The First VF Offset and VF Stride fields depend on the NumVFs setting, so
refresh the cached fields in struct pci_sriov when updating NumVFs.  See
the SR-IOV spec r1.1, sec 3.3.9 and 3.3.10.

[bhelgaas: changelog, remove kernel-doc comment marker]
Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>