fix bug when total_training_steps is not specified

If `total_training_steps` is not specified, the default will be -1.
Thus checking whether it is > 0 is needed

dlio_benchmark/main.py

@@ -257,7 +257,7 @@ def _train(self, epoch):
         loader = self.framework.get_loader(dataset_type=DatasetType.TRAIN)
         t0 = time()
         for batch in dlp.iter(loader.next()):
-            if overall_step > max_steps or overall_step > self.total_training_steps:
+            if overall_step > max_steps or ((self.total_training_steps > 0) and (overall_step > self.total_training_steps)):
                 if self.args.my_rank == 0:
                     logging.info(f"{utcnow()} Maximum number of steps reached")
                 if (block_step != 1 and self.do_checkpoint) or (not self.do_checkpoint):