PCI: layerscape: Use of_device_get_match_data() to simplify probe

The only way to call ls_pcie_probe() is to match an entry in
ls_pcie_of_match[], so match cannot be NULL.

Use of_device_get_match_data() to retrieve the drvdata pointer.  No
functional change intended.

Based-on-suggestion-from: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>