[fp16/doc] correct initial_scale_power default value (#3275)

docs/_pages/config-json.md

@@ -250,7 +250,7 @@ Example of <i>**scheduler**</i>
 
 | Description                                                                                                                                                                                             | Default |
 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------- |
-| <i>**initial_scale_power**</i> is a **fp16** parameter representing the power of the initial dynamic loss scale value. The actual loss scale is computed as 2<sup><i>**initial_scale_power**</i></sup>. | `32`    |
+| <i>**initial_scale_power**</i> is a **fp16** parameter representing the power of the initial dynamic loss scale value. The actual loss scale is computed as 2<sup><i>**initial_scale_power**</i></sup>. | `16`    |
 
 <i>**fp16:loss_scale_window**</i>: [integer]