PCI/VPD: Make pci_vpd_wait() uninterruptible

Reading/writing 4 bytes should be fast enough even on a slow bus, therefore
pci_vpd_wait() doesn't have to be interruptible.  Making it uninterruptible
allows to simplify the code.

In addition make VPD writes uninterruptible in general.  It's about vital
data, and allowing writes to be interruptible may leave the VPD in an
inconsistent state.

Link: https://lore.kernel.org/r/258bf994-bc2a-2907-9181-2c7a562986d5@gmail.com
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>