dt-bindings: display: msm: Drop type from 'memory-region'

'memory-region' is a common property and already has a type.

Link: https://lore.kernel.org/r/20230125221357.3057655-1-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/display/msm/gpu.yaml

@@ -89,7 +89,7 @@ properties:
       help bring the GPU out of secure mode.
     properties:
       memory-region:
-        $ref: /schemas/types.yaml#/definitions/phandle
+        maxItems: 1
 
       firmware-name:
         description: |