dt-bindings: ak4554: extension should be .txt

Signed-off-by: Raphaël Poggi <poggi.raph@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>

diff --git a/Documentation/devicetree/bindings/sound/ak4554.c b/Documentation/devicetree/bindings/sound/ak4554.txt
similarity index 100%
rename from Documentation/devicetree/bindings/sound/ak4554.c
rename to Documentation/devicetree/bindings/sound/ak4554.txt