net: amlogic,meson-dwmac: Fix "amlogic,tx-delay-ns" schema

The "amlogic,tx-delay-ns" property schema has unnecessary type reference
as it's a standard unit suffix, and the constraints are in freeform
text rather than schema.
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://patch.msgid.link/20240909172342.487675-2-robh@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/amlogic,meson-dwmac.yaml

@@ -58,18 +58,18 @@ allOf:
             - const: timing-adjustment
 
         amlogic,tx-delay-ns:
-          $ref: /schemas/types.yaml#/definitions/uint32
+          enum: [0, 2, 4, 6]
+          default: 2
           description:
-            The internal RGMII TX clock delay (provided by this driver) in
-            nanoseconds. Allowed values are 0ns, 2ns, 4ns, 6ns.
-            When phy-mode is set to "rgmii" then the TX delay should be
-            explicitly configured. When not configured a fallback of 2ns is
-            used. When the phy-mode is set to either "rgmii-id" or "rgmii-txid"
-            the TX clock delay is already provided by the PHY. In that case
-            this property should be set to 0ns (which disables the TX clock
-            delay in the MAC to prevent the clock from going off because both
-            PHY and MAC are adding a delay).
-            Any configuration is ignored when the phy-mode is set to "rmii".
+            The internal RGMII TX clock delay (provided by this driver)
+            in nanoseconds. When phy-mode is set to "rgmii" then the TX
+            delay should be explicitly configured. When the phy-mode is
+            set to either "rgmii-id" or "rgmii-txid" the TX clock delay
+            is already provided by the PHY. In that case this property
+            should be set to 0ns (which disables the TX clock delay in
+            the MAC to prevent the clock from going off because both
+            PHY and MAC are adding a delay). Any configuration is
+            ignored when the phy-mode is set to "rmii".
 
         amlogic,rx-delay-ns:
           deprecated: true