PCI: layerscape: Fix drvdata usage before assignment

Commit fefe6733 ("PCI: layerscape: Move struct pcie_port setup
to probe function") changed the init ordering of the pcie structure,
but started to use the pcie->drvdata field before initializing it.
Mayhem follows.

Fix this by moving the drvdata assignment right before the first use.
Tested on LS2085a.

Fixes: efe6733e516 ("PCI: layerscape: Move struct pcie_port setup to probe function")
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>