dt-bindings: net: hirschmann,hellcreek: use absolute path to other schema

Absolute path to other DT schema is preferred over relative one.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Acked-by: Kurt Kanzenbach <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/devicetree/bindings/net/dsa/hirschmann,hellcreek.yaml

···
       "^led@[01]$":
         type: object
         description: Hellcreek leds
-        $ref: ../../leds/common.yaml#
+        $ref: /schemas/leds/common.yaml#
 
         properties:
           reg: