PCI/PM: Clear state_saved during suspend

This patch clears pci_dev->state_saved at the beginning of suspending.
PCI config state may be saved long before that.  Some drivers call
pci_save_state() from the ->probe() callback to get snapshot of sane
configuration space to use in the ->slot_reset() callback.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org> # add comment
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>