dt-bindings: net: sparx5: Narrow properly LAN969x register space windows

Commit 267bca002c50 ("dt-bindings: net: sparx5: correct LAN969x register
space windows") said that LAN969x has exactly two address spaces ("reg"
property) but implemented it as 2 or more. Narrow the constraint to
properly express that only two items are allowed, which also matches
Linux driver.

Fixes: 267bca002c50 ("dt-bindings: net: sparx5: correct LAN969x register space windows")
Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

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

···
     then:
       properties:
         reg:
-          minItems: 2
+          maxItems: 2
         reg-names:
-          minItems: 2
+          maxItems: 2
     else:
       properties:
         reg: