dt-bindings: pwm: allwinner,sun4i-a10-pwm: add top-level constraints

Properties with variable number of items per each device are expected to
have widest constraints in top-level "properties:" block and further
customized (narrowed) in "if:then:".  Add missing top-level constraints
for clock-names.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20240818172828.121728-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Uwe Kleine-König <ukleinek@kernel.org>

Documentation/devicetree/bindings/pwm/allwinner,sun4i-a10-pwm.yaml

@@ -46,10 +46,11 @@ properties:
       - description: Module Clock
       - description: Bus Clock
 
-  # Even though it only applies to subschemas under the conditionals,
-  # not listing them here will trigger a warning because of the
-  # additionalsProperties set to false.
-  clock-names: true
+  clock-names:
+    minItems: 1
+    items:
+      - const: mod
+      - const: bus
 
   resets:
     maxItems: 1