fix bugs in gat training script (#3505)

Co-authored-by: Jinjing Zhou <VoVAllen@users.noreply.github.com>
Co-authored-by: Zihao Ye <expye@outlook.com>

examples/pytorch/gat/train.py

@@ -107,6 +107,7 @@ def main(args):
     for epoch in range(args.epochs):
         model.train()
         if epoch >= 3:
+            torch.cuda.synchronize()
             t0 = time.time()
         # forward
         logits = model(features)
@@ -117,6 +118,7 @@ def main(args):
         optimizer.step()
 
         if epoch >= 3:
+            torch.cuda.synchronize()
             dur.append(time.time() - t0)
 
         train_acc = accuracy(logits[train_mask], labels[train_mask])