PCI: pci-driver: convert to use DRIVER_ATTR_WO

We are trying to get rid of DRIVER_ATTR(), and all of the pci-driver
core driver attributes can be trivially changed to use DRIVER_ATTR_WO().

Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: <linux-pci@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>