dt-bindings: net: sparx5: correct LAN969x register space windows

LAN969x needs only 2 register space windows as GCB is already covered by
the "devices" register space window, so expect only 2 "reg" and "reg-names"
properties.

Fixes: 41c6439fdc ("dt-bindings: net: add compatible strings for lan969x targets")
Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20250925132109.583984-1-robert.marko@sartura.hr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/microchip,sparx5-switch.yaml

@@ -55,12 +55,14 @@ properties:
           - const: microchip,lan9691-switch
 
   reg:
+    minItems: 2
     items:
       - description: cpu target
       - description: devices target
       - description: general control block target
 
   reg-names:
+    minItems: 2
     items:
       - const: cpu
       - const: devices
@@ -168,6 +170,26 @@ required:
   - interrupt-names
   - ethernet-ports
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - microchip,lan9691-switch
+    then:
+      properties:
+        reg:
+          minItems: 2
+        reg-names:
+          minItems: 2
+    else:
+      properties:
+        reg:
+          minItems: 3
+        reg-names:
+          minItems: 3
+
 additionalProperties: false
 
 examples: