PCI/VPD: Reorder pci_read_vpd(), pci_write_vpd()

Reorder pci_read_vpd() and pci_write_vpd() to prepare for future patches.
No functional change intended.

Link: https://lore.kernel.org/r/89f0f5a2-293b-a017-fc67-a36473a792bf@gmail.com
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>