ultralytics 8.0.216 fix hard-coded batch=64 cls loss (#6523)

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: HDW AI group <huzhongshan@gmail.com>

ultralytics/utils/loss.py

@@ -523,6 +523,6 @@ class v8ClassificationLoss:
 
     def __call__(self, preds, batch):
         """Compute the classification loss between predictions and true labels."""
-        loss = torch.nn.functional.cross_entropy(preds, batch['cls'], reduction='sum') / 64
+        loss = torch.nn.functional.cross_entropy(preds, batch['cls'], reduction='mean')
         loss_items = loss.detach()
         return loss, loss_items