dt-bindings: watchdog: Add missing clocks requirement in Samsung SoC watchdog

The Samsung SoC watchdog driver always required providing a clock
(either through platform data or from DT).  However when bindings were
added in commit 9487a9cc ("watchdog: s3c2410: Add support for device
tree based probe"), they missed the requirement of clock.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/watchdog/samsung-wdt.yaml

@@ -26,6 +26,13 @@ properties:
   reg:
     maxItems: 1
 
+  clocks:
+    maxItems: 1
+
+  clock-names:
+    items:
+      - const: watchdog
+
   interrupts:
     maxItems: 1
 
@@ -37,6 +44,8 @@ properties:
 
 required:
   - compatible
+  - clocks
+  - clock-names
   - interrupts
   - reg