PCI: layerscape: Remove unnecessary class code fixup

Now that the Class Code fixup in dw_pcie_setup_rc() works, remove the fixup
from the Layerscape driver.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Roy Zang <tie-fei.zang@freescale.com>