ASoC: max9877: Remove unused function declaration

Remove unused function declaration from header
Signed-off-by: Helen Koike <helen.koike@collabora.co.uk>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/max9877.h

@@ -32,6 +32,4 @@
 #define MAX9877_BYPASS			(1 << 6)
 #define MAX9877_SHDN			(1 << 7)
 
-extern int max9877_add_controls(struct snd_soc_codec *codec);
-
 #endif