ARM: ux500: Add RTC (fixed-frequency) clock node to DBx500 Device Tree

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

arch/arm/boot/dts/ste-dbx5x0.dtsi

@@ -57,6 +57,10 @@ prcc_pclk: prcc-periph-clock {
 			prcc_kclk: prcc-kernel-clock {
 				#clock-cells = <2>;
 			};
+
+			rtc_clk: rtc32k-clock {
+				#clock-cells = <0>;
+			};
 		};
 
 		timer@a0410600 {