Update data_performance.ipynb

Reverted the changes as mentioned.

Author: RenuPatelGoogle

site/en/guide/data_performance.ipynb

@@ -275,7 +275,7 @@
         "### Prefetching\n",
         "\n",
         "Prefetching overlaps the preprocessing and model execution of a training step.\n",
-        "While the model is executing training `steps`, the input pipeline is reading the data for `steps+1`.\n",
+        "While the model is executing training step `s`, the input pipeline is reading the data for step `s+1`.\n",
         "Doing so reduces the step time to the maximum (as opposed to the sum) of the training and the time it takes to extract the data.\n",
         "\n",
         "The `tf.data` API provides the `tf.data.Dataset.prefetch` transformation.\n",