[Bugfix] Fix conditional judgment of cuda (#4026) (#4027)

examples/pytorch/gat/train.py

@@ -107,6 +107,7 @@ def main(args):
     for epoch in range(args.epochs):
         model.train()
         if epoch >= 3:
+            if cuda:
                 torch.cuda.synchronize()
             t0 = time.time()
         # forward
@@ -118,6 +119,7 @@ def main(args):
         optimizer.step()
 
         if epoch >= 3:
+            if cuda:
                 torch.cuda.synchronize()
             dur.append(time.time() - t0)