ASoC: tfa9879: add DT bindings to MAINTAINERS

Let's keep maintenance of the driver and the bindings in one place.
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Mark Brown <broonie@kernel.org>

MAINTAINERS

@@ -9805,6 +9805,7 @@ NXP TFA9879 DRIVER
 M:	Peter Rosin <peda@axentia.se>
 L:	alsa-devel@alsa-project.org (moderated for non-subscribers)
 S:	Maintained
+F:	Documentation/devicetree/bindings/sound/tfa9879.txt
 F:	sound/soc/codecs/tfa9879*
 
 NXP-NCI NFC DRIVER