PCI/AER: Work around use-after-free in pcie_do_fatal_recovery()

When an fatal error is received by a non-bridge device, the device is
removed, and pci_stop_and_remove_bus_device() deallocates the device
structure.  The freed device structure is used by subsequent code to send
uevents and print messages.

Hold a reference on the device until we're finished using it.  This is not
an ideal fix because pcie_do_fatal_recovery() should not use the device at
all after removing it, but that's too big a project for right now.

Fixes: 7e9084b3 ("PCI/AER: Handle ERR_FATAL with removal and re-enumeration of devices")
Signed-off-by: Thomas Tai <thomas.tai@oracle.com>
[bhelgaas: changelog, reduce get/put coverage]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>