ASoC: wm8904: Use WARN_ON() instead of BUG_ON()

Use WARN_ON() and handle the error cases accordingly.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NMark Brown <broonie@linaro.org>

sound/soc/codecs/wm8904.c

@@ -658,7 +658,8 @@ SOC_SINGLE_TLV("EQ5 Volume", WM8904_EQ6, 0, 24, 0, eq_tlv),
 static int cp_event(struct snd_soc_dapm_widget *w,
 		    struct snd_kcontrol *kcontrol, int event)
 {
-	BUG_ON(event != SND_SOC_DAPM_POST_PMU);
+	if (WARN_ON(event != SND_SOC_DAPM_POST_PMU))
+		return -EINVAL;
 
 	/* Maximum startup time */
 	udelay(500);