[OpenVINOQuantizer] return annotated model (#3263)

### Changes

Mode return is added to `annotate` method of the OpenVINOQuantizer

### Reason for changes

To align with the signature

Author: daniil-lyakhov

nncf/experimental/torch/fx/quantization/quantizer/openvino_quantizer.py

@@ -154,6 +154,7 @@ def annotate(self, model: torch.fx.GraphModule) -> torch.fx.GraphModule:
         for node, annotation in node_vs_torch_annotation.items():
             assert QUANT_ANNOTATION_KEY not in node.meta
             node.meta[QUANT_ANNOTATION_KEY] = annotation
+        return model
 
     @staticmethod
     def _get_unified_scales_root_quantizer_id(