arm64: dts: zynqmp: Fix node names which contain "_"

s/_/-/ for node names.

It fixes warnings like this:
... Warning (node_name_chars_strict): /cpu_opp_table:
Character '_' not recommended in node name ...

Issues reported by make dtbs W=12

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/dts/zynqmp-zcu111-revA.dts b/arch/arm/dts/zynqmp-zcu111-revA.dts
index ca95d7e..5b648ce 100644
--- a/arch/arm/dts/zynqmp-zcu111-revA.dts
+++ b/arch/arm/dts/zynqmp-zcu111-revA.dts
@@ -58,7 +58,7 @@
 
 	leds {
 		compatible = "gpio-leds";
-		heartbeat_led {
+		heartbeat-led {
 			label = "heartbeat";
 			gpios = <&gpio 23 GPIO_ACTIVE_HIGH>;
 			linux,default-trigger = "heartbeat";