Revert "PCI: Remove struct pci_dev->driver"

This reverts commit b5f9c644.

Revert b5f9c644 ("PCI: Remove struct pci_dev->driver"), which is needed
to revert 2a4d9408 ("PCI: Use to_pci_driver() instead of
pci_dev->driver").

2a4d9408 caused a NULL pointer dereference reported by Robert Święcki.
Details in the revert of that commit.

Fixes: 2a4d9408 ("PCI: Use to_pci_driver() instead of pci_dev->driver")
Link: https://lore.kernel.org/linux-i2c/CAP145pgdrdiMAT7=-iB1DMgA7t_bMqTcJL4N0=6u8kNY3EU0dw@mail.gmail.com/


Reported-by: Robert Święcki <robert@swiecki.net>
Tested-by: Robert Święcki <robert@swiecki.net>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>