ARM: tegra: paz: add backlight power supply

Select default 3.3V, shouldn't do any harm.

Fixes warning:
arch/arm/boot/dts/tegra20-paz.dt.yaml: backlight: 'power-supply' is a required property
	From schema: /home/runner/work/linux/linux/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.yaml

Signed-off-by: David Heidelberg <david@ixit.cz>

arch/arm/boot/dts/tegra20-paz00.dts

@@ -620,6 +620,7 @@
 
 		enable-gpios = <&gpio TEGRA_GPIO(U, 4) GPIO_ACTIVE_HIGH>;
 		pwms = <&pwm 0 5000000>;
+		power-supply = <&vdd_pnl_reg>;
 
 		brightness-levels = <0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 255>;
 		default-brightness-level = <10>;