boards: st: fix STM3U0 boards DTS files coding style

Fix board DTS coding style issues to prevent they spread when a	new
board is introduced and used this DTS as example start point.

Issues addressed from Zephyr devicetree style guidelines [1]:
- Insert a single empty line to separate nodes at the same hierarchy level.

No functional change.

Link: https://docs.zephyrproject.org/latest/contribute/style/devicetree.html [1]
Signed-off-by: Etienne Carriere <[email protected]>

Author: etienne-lms

boards/st/nucleo_u031r8/nucleo_u031r8.dts

@@ -26,6 +26,7 @@
 
 	leds: leds {
 		compatible = "gpio-leds";
+
 		green_led_1: led_1 {
 			gpios = <&gpioa 5 GPIO_ACTIVE_HIGH>;
 			label = "User LD4";
@@ -34,6 +35,7 @@
 
 	gpio_keys {
 		compatible = "gpio-keys";
+
 		user_button: button {
 			label = "User";
 			gpios = <&gpioc 13 GPIO_ACTIVE_HIGH>;

boards/st/nucleo_u083rc/nucleo_u083rc.dts

@@ -26,6 +26,7 @@
 
 	leds: leds {
 		compatible = "gpio-leds";
+
 		green_led_1: led_4 {
 			gpios = <&gpioa 5 GPIO_ACTIVE_HIGH>;
 			label = "User LD4";
@@ -34,6 +35,7 @@
 
 	gpio_keys {
 		compatible = "gpio-keys";
+
 		user_button: button {
 			label = "User";
 			gpios = <&gpioc 13 GPIO_ACTIVE_HIGH>;

boards/st/stm32u083c_dk/stm32u083c_dk.dts

@@ -27,6 +27,7 @@
 
 	leds: leds {
 		compatible = "gpio-leds";
+
 		green_led_1: led_3 {
 			gpios = <&gpioc 13 GPIO_ACTIVE_HIGH>;
 			label = "User LD3";
@@ -157,6 +158,7 @@
 		group = <6>;
 		channel-ios = <TSC_IO2>;
 		sampling-io = <TSC_IO1>;
+
 		ts1 {
 			compatible = "tsc-keys";
 			sampling-interval-ms = <10>;