PCI: rockchip: Fix negotiated lanes calculation

The calculation of negotiated lanes is wrong: it should be shifted by
PCIE_CORE_PL_CONF_LANE_SHIFT, but it is shifted by
PCIE_CORE_PL_CONF_LANE_MASK instead.  Let's fix it.

Fixes: e77f847d ("PCI: rockchip: Add Rockchip PCIe controller support")
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>