fix Tensor.numpy()[0] to float(Tensor) to adapt 0D (#2884)

Author: zhwesky2010

examples/tess/cls0/local/train.py

@@ -121,7 +121,7 @@ def _collate_features(batch):
             optimizer.clear_grad()
 
             # Calculate loss
-            avg_loss += loss.numpy()[0]
+            avg_loss += float(loss)
 
             # Calculate metrics
             preds = paddle.argmax(logits, axis=1)