PCI: Return -ENOSYS for SR-IOV operations on non-SR-IOV devices

Change the return value to -ENOSYS if a device is not an SR-IOV PF.
Previously we returned either -ENODEV or -EINVAL.

Also have pci_sriov_get_totalvfs() return 0 in the error case to make the
behaviour consistent whether CONFIG_PCI_IOV is enabled or not.

Signed-off-by: Stefan Assmann <sassmann@kpanic.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>