ASoC: rt5645: fix implicit declaration error

kbuild robot reports a implicit declaration of function
'rt5645_irq_detection' error.
Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/rt5645.c

@@ -2535,6 +2535,8 @@ static int rt5645_jack_detect(struct snd_soc_codec *codec, int jack_insert)
 	return rt5645->jack_type;
 }
 
+static int rt5645_irq_detection(struct rt5645_priv *rt5645);
+
 int rt5645_set_jack_detect(struct snd_soc_codec *codec,
 	struct snd_soc_jack *hp_jack, struct snd_soc_jack *mic_jack,
 	struct snd_soc_jack *btn_jack)