Docs: Actually fix 2.1.2 release notes build

The readme file is all uppercase letters, so it must be referenced
that way.

Change-Id: Ia54e6234c2aa19f076dc72f9602adcfacd77627f
Signed-off-by: Tomi Fontanilles <[email protected]>
(cherry picked from commit 5d9f340feb9d8fb7ff7e582a7087a8b20f0cea0c)

Author: tomi-font

docs/releases/2.1.2.rst

@@ -10,7 +10,7 @@ New features
 New platforms supported
 =======================
 
-- :doc:`MAX32657 </platform/adi/max32657/readme>`
+ - :doc:`MAX32657 </platform/adi/max32657/README>`
 
 Hotfixes
 ========