arm64: dts: exynos: add ADC supply on Exynos7 Espresso

ADC requires supply and it seems LDO3 (same as on Exynos5433 TM2 boards)
fits in voltage range of 1.8 V.  Use it to silence warning:

  exynos7-espresso.dtb: adc@13620000: 'vdd-supply' is a required property

Link: https://lore.kernel.org/r/20230120173116.341270-2-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>

arch/arm64/boot/dts/exynos/exynos7-espresso.dts

@@ -78,6 +78,7 @@ &watchdog {
 };
 
 &adc {
+	vdd-supply = <&ldo3_reg>;
 	status = "okay";
 };