arm64: dts: rockchip: change clkreq mode for rk3399-firefly

pcie_clkreqn actually doesn't work at all, so replace it with
pcie_clkreqn_cpm.
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3399-firefly.dts

@@ -550,7 +550,7 @@ &pcie0 {
 	ep-gpios = <&gpio4 RK_PD1 GPIO_ACTIVE_HIGH>;
 	num-lanes = <4>;
 	pinctrl-names = "default";
-	pinctrl-0 = <&pcie_clkreqn>;
+	pinctrl-0 = <&pcie_clkreqn_cpm>;
 	status = "okay";
 };