Revert "PCI: Remove struct pci_dev->driver"

Revert "PCI: Remove struct pci_dev->driver"

This reverts commit 73eaf9edca5506842ee8bbe9d857a76d3519c922.

Revert 73eaf9edca55 ("PCI: Remove struct pci_dev->driver"), which is needed
to revert eed08cea8988 ("PCI: Use to_pci_driver() instead of
pci_dev->driver").

eed08cea8988 caused a NULL pointer dereference reported by Robert Święcki.
Details in the revert of that commit.

Fixes: eed08cea8988 ("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>