arm64: dts: rockchip: remove PCIe assigned-clocks in excavator baseboard

Reference clock is needed for pcie_phy, not pcie controller.
Actually pcie_phy doesn't need this since rk3399 clock driver
already take care of this.

Suggested-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Vicente Bergas <vicencb@gmail.com>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>