samples: Fix fs format sample README to correct a formatting problem

The Sample Output section is missing a blank line before the code block
markup, resulting in the sample output text showing up with an incorrect
format. Fixed by adding a blank line.

Signed-off-by: Irfan Ahmad <[email protected]>

Author: hIAhmad

samples/subsys/fs/format/README.rst

@@ -45,6 +45,7 @@ Sample Output
 =============
 
 When the sample runs successfully you should see following message on the screen:
+
 .. code-block:: console
 
   I: LittleFS version 2.4, disk version 2.0