Update loss for FP16 tobj (#7088)

utils/loss.py

@@ -125,7 +125,7 @@ class ComputeLoss:
         # Losses
         for i, pi in enumerate(p):  # layer index, layer predictions
             b, a, gj, gi = indices[i]  # image, anchor, gridy, gridx
-            tobj = torch.zeros(pi.shape[:4], device=self.device)  # target obj
+            tobj = torch.zeros(pi.shape[:4], dtype=pi.dtype, device=self.device)  # target obj
 
             n = b.shape[0]  # number of targets
             if n: