ASoC: soc-core: return true, false in snd_soc_volsw_is_stereo()

Fix the following coccicheck warning:

include/sound/soc.h:1271:9-10: WARNING: return of 0/1 in function
'snd_soc_volsw_is_stereo' with return type bool
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Link: https://lore.kernel.org/r/20200422071805.48793-1-yanaijie@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>

include/sound/soc.h

@@ -1270,13 +1270,13 @@ static inline void *snd_soc_card_get_drvdata(struct snd_soc_card *card)
 static inline bool snd_soc_volsw_is_stereo(struct soc_mixer_control *mc)
 {
 	if (mc->reg == mc->rreg && mc->shift == mc->rshift)
-		return 0;
+		return false;
 	/*
 	 * mc->reg == mc->rreg && mc->shift != mc->rshift, or
 	 * mc->reg != mc->rreg means that the control is
 	 * stereo (bits in one register or in two registers)
 	 */
-	return 1;
+	return true;
 }
 
 static inline unsigned int snd_soc_enum_val_to_item(struct soc_enum *e,