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 9487a9cc7140 ("watchdog: s3c2410: Add support for device
tree based probe"), they missed the requirement of clock.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>

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

···
   reg:
     maxItems: 1
 
+  clocks:
+    maxItems: 1
+
+  clock-names:
+    items:
+      - const: watchdog
+
   interrupts:
     maxItems: 1
 
···
 
 required:
   - compatible
+  - clocks
+  - clock-names
   - interrupts
   - reg