dt-bindings: samsung: exynos-usi: add missing 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 reg, clocks and clock-names.
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20240818172804.121666-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Documentation/devicetree/bindings/soc/samsung/exynos-usi.yaml

@@ -32,11 +32,16 @@ properties:
       - enum:
           - samsung,exynos850-usi
 
-  reg: true
+  reg:
+    maxItems: 1
 
-  clocks: true
+  clocks:
+    maxItems: 2
 
-  clock-names: true
+  clock-names:
+    items:
+      - const: pclk
+      - const: ipclk
 
   ranges: true
 
@@ -113,9 +118,7 @@ then:
         - description: Operating clock for UART/SPI/I2C protocol
 
     clock-names:
-      items:
-        - const: pclk
-        - const: ipclk
+      maxItems: 2
 
   required:
     - reg