ASoC: sgtl5000: Do a sanity check on SYS_MCLK

According to the sgtl5000 datasheet the valid range for SYS_MCLK is from 8 to
27 MHz.

Add a sanity check prior to enabling SYS_MCLK.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: NMark Brown <broonie@kernel.org>

sound/soc/codecs/sgtl5000.c

@@ -1445,6 +1445,7 @@ static int sgtl5000_i2c_probe(struct i2c_client *client,
 {
 	struct sgtl5000_priv *sgtl5000;
 	int ret, reg, rev;
+	unsigned int mclk;
 
 	sgtl5000 = devm_kzalloc(&client->dev, sizeof(struct sgtl5000_priv),
 								GFP_KERNEL);
@@ -1468,6 +1469,14 @@ static int sgtl5000_i2c_probe(struct i2c_client *client,
 		return ret;
 	}
 
+	/* SGTL5000 SYS_MCLK should be between 8 and 27 MHz */
+	mclk = clk_get_rate(sgtl5000->mclk);
+	if (mclk < 8000000 || mclk > 27000000) {
+		dev_err(&client->dev, "Invalid SYS_CLK frequency: %u.%03uMHz\n",
+			mclk / 1000000, mclk / 1000 % 1000);
+		return -EINVAL;
+	}
+
 	ret = clk_prepare_enable(sgtl5000->mclk);
 	if (ret)
 		return ret;