IB/ipath: Use pci_dev->revision, again

Commit 44c10138 ("PCI: Change all drivers to use pci_device->revision")
already converted this driver to using the revision field of struct
pci_dev but commit bb917144 ("IB/ipath: Misc changes to prepare
for IB7220 introduction") later reverted that change for some strange
reason.  Restore the change.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Acked-by: Mike Marciniszyn <mike.marciniszyn@qlogic.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>