PCI: Remove struct pci_dev->driver

There are no remaining uses of the struct pci_dev->driver pointer, so
remove it.

Link: https://lore.kernel.org/r/20211004125935.2300113-12-u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>