SavedModel TF Serve Fix (#7228)

* SavedModel TF Serve Fix

Fix for https://github.com/ultralytics/yolov5/issues/7205 proposed by @tylertroy

* Update export.py

export.py

         if keras:
             keras_model.save(f, save_format='tf')
         else:
-            m = tf.function(lambda x: keras_model(x))  # full model
             spec = tf.TensorSpec(keras_model.inputs[0].shape, keras_model.inputs[0].dtype)
+            m = tf.function(lambda x: keras_model(x))  # full model
             m = m.get_concrete_function(spec)
             frozen_func = convert_variables_to_constants_v2(m)
             tfm = tf.Module()
-            tfm.__call__ = tf.function(lambda x: frozen_func(x)[0], [spec])
+            tfm.__call__ = tf.function(lambda x: frozen_func(x)[:4] if tf_nms else frozen_func(x)[0], [spec])
             tfm.__call__(im)
             tf.saved_model.save(tfm,
                                 f,