Fix VMSTATE_PCI_DEVICE version

Fix VMSTATE_PCI_DEVICE version

PCI device entries have to have a default version, not 2, because they are
used in the midle of other structures that can have _any_ version number.

We can't use proper versioning here until we have SubSections support.
Why we didn't noticed before?  Because in a PC, the only device ported with
a version less that 2 is piix_pm, and for that one, default pci values are
right.  If you use a virtio-console, you will see that its state it is not
loaded back.

Thanks to Amit Shah for reporting the problem and help debug the fix.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>