dt: bcm6858: watchdog should use a 50Mhz clock

The watchdog should use a clock at 50 Mhz, so
instead of using the clock osc (200 Mhz), we
define a reference clock at 50Mhz and use it
for both watchdog.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
Reviewed-by: Stefan Roese <sr@denx.de>

arch/arm/dts/bcm6858.dtsi

@@ -66,6 +66,12 @@
 			clock-frequency = <200000000>;
 			u-boot,dm-pre-reloc;
 		};
+
+		refclk50mhz: refclk50mhz {
+			compatible = "fixed-clock";
+			#clock-cells = <0>;
+			clock-frequency = <50000000>;
+		};
 	};
 
 	ubus {
@@ -92,13 +98,13 @@
 		wdt1: watchdog@ff802780 {
 			compatible = "brcm,bcm6345-wdt";
 			reg = <0x0 0xff802780 0x0 0x14>;
-			clocks = <&periph_osc>;
+			clocks = <&refclk50mhz>;
 		};
 
 		wdt2: watchdog@ff8027c0 {
 			compatible = "brcm,bcm6345-wdt";
 			reg = <0x0 0xff8027c0 0x0 0x14>;
-			clocks = <&periph_osc>;
+			clocks = <&refclk50mhz>;
 		};
 
 		wdt-reboot {