Fix batch size calculation in dist_tuto (#2754)

Batch size must be an int, not a float. This change fixes it, basically doing the same as in https://github.com/seba-1511/dist_tuto.pth/blob/a552567061a9985cdcfe72ecb9b47e4630d6a7fe/train_dist.py#L85.

Co-authored-by: Svetlana Karslioglu <[email protected]>

intermediate_source/dist_tuto.rst

@@ -327,7 +327,7 @@ the following few lines:
                                      transforms.Normalize((0.1307,), (0.3081,))
                                  ]))
         size = dist.get_world_size()
-        bsz = 128 / float(size)
+        bsz = 128 // size
         partition_sizes = [1.0 / size for _ in range(size)]
         partition = DataPartitioner(dataset, partition_sizes)
         partition = partition.use(dist.get_rank())