arm: dts: am33xx.dtsi: Add node name to rtc device node

Making it possible to reference and therefor change (disable) this
device node from other dts file which import this dtsi file.
Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Lukas Stockmann <lukas.stockmann@siemens.com>
Cc: Benoit Cousson <bcousson@baylibre.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am33xx.dtsi

@@ -404,7 +404,7 @@ timer7: timer@4804a000 {
 			ti,timer-pwm;
 		};
 
-		rtc@44e3e000 {
+		rtc: rtc@44e3e000 {
 			compatible = "ti,da830-rtc";
 			reg = <0x44e3e000 0x1000>;
 			interrupts = <75