Fix link in DataFlashBlockDevice.md

Fix broken link now that Doxygen's fixed.

Author: Amanda Butler

docs/reference/api/storage/DataFlashBlockDevice.md

@@ -8,7 +8,7 @@ You can configure the DataFlashBlockDevice to force the underlying device to use
 
 ### DataFlashBlockDevice class reference
 
-<!--- [![View code](https://www.mbed.com/embed/?type=library)](<Should be added after doxygen run>) --->
+[![View code](https://www.mbed.com/embed/?type=library)](http://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/class_data_flash_block_device.html)
 
 ### DataFlashBlockDevice example: