dt-bindings: net: ipq4019-mdio: document required clock-names

IPQ5018, IPQ6018 and IPQ8074 require clock-names to be set as driver is
requesting the clock based on it and not index, so document that and make
it required for the listed SoC-s.
Signed-off-by: Robert Marko <robimarko@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221114194734.3287854-4-robimarko@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/qcom,ipq4019-mdio.yaml

@@ -40,6 +40,10 @@ properties:
     items:
       - description: MDIO clock source frequency fixed to 100MHZ
 
+  clock-names:
+    items:
+      - const: gcc_mdio_ahb_clk
+
 required:
   - compatible
   - reg
@@ -60,9 +64,11 @@ allOf:
     then:
       required:
         - clocks
+        - clock-names
     else:
       properties:
         clocks: false
+        clock-names: false
 
 unevaluatedProperties: false