pcie_flr() saves and restores nothing; pairing it with
pci_save_state() and pci_restore_state() is the caller's job. On the
DEVF_RESET_DETACH path of pci_reset_child(), device_detach() saves
through pci_child_detached() and nothing restores. The only restore,
BUS_RESET_POST(), runs when pcie_flr() reports that no reset was
performed.

An FLR returns configuration space to its defaults, so the reprobe
runs against a function whose BARs read zero.

Restore the saved state before reprobing.