ASoC: sgtl5000: guide user when regulator support is needed

Print a hint when the user has a setup where CONFIG_REGULATOR is really
needed to make the driver work.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Tested-by: Dong Aisheng <b29396@freescale.com>
Tested-by: Shawn Guo <shawn.guo@freescale.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/sgtl5000.c

@@ -907,6 +907,7 @@ static int ldo_regulator_register(struct snd_soc_codec *codec,
 				struct regulator_init_data *init_data,
 				int voltage)
 {
+	dev_err(codec->dev, "this setup needs regulator support in the kernel\n");
 	return -EINVAL;
 }