dt-bindings: net: qcom,ipa: Drop unnecessary type ref on 'memory-region'

'memory-region' is a common property, so it doesn't need a type ref here.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Alex Elder <elder@kernel.org>
Cc: netdev@vger.kernel.org
Acked-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20201222040121.1314370-1-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/net/qcom,ipa.yaml

@@ -121,7 +121,6 @@ properties:
       receive and act on notifications of modem up/down events.
 
   memory-region:
-    $ref: /schemas/types.yaml#/definitions/phandle-array
     maxItems: 1
     description:
       If present, a phandle for a reserved memory area that holds