lantiq: AVM Fritz 736x: fix PCIe reset GPIO

The vr9.dtsi configures the GPIO 38 as reset GPIO. Also the fon LED is
configured on GPIO 38. This conflicts and makes the probing of the PCIe
controller fail in OpenWrt 25.12.

The AVM GPL source code configured GPIO 21 as PCIe reset.

Fixes: https://github.com/openwrt/openwrt/issues/21562
Link: https://github.com/openwrt/openwrt/pull/21641
Signed-off-by: Hauke Mehrtens <[email protected]>
(cherry picked from commit a4285d7cc092c0d0bd8fccd4b9eebdbfbd6e8ca4)

target/linux/lantiq/files/arch/mips/boot/dts/lantiq/vr9_avm_fritz736x.dtsi

@@ -156,6 +156,7 @@
 
 &pcie0 {
 	status = "okay";
+	gpio-reset = <&gpio 21 GPIO_ACTIVE_LOW>;
 
 	pcie@0 {
 		reg = <0 0 0 0 0>;