iwlwifi: use pci_dev->revision, again

iwlwifi: use pci_dev->revision, again

Commit c5390376c5ac067e3c16c483a22668ac40dcc0e5 (net: use pci_dev->revision,
again) already converted this driver to using the 'revision' field of 'struct
pci_dev' but commit ca8b5f2c82d1979880dc5252d9c6ec3bcdf41184 (iwlagn: move PCI
related operations from probe and remove to PCI layer) has again added the code
to read the PCI revision ID register...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>