ASoC: kirkwood: prefer external clock over internal clock

When there is an external clock, always use this one.
This prevents the two Dove audio devices to use the same DCO clock
at different rates.
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/kirkwood/kirkwood-i2s.c

@@ -103,7 +103,7 @@ static void kirkwood_set_rate(struct snd_soc_dai *dai,
 {
 	uint32_t clks_ctrl;
 
-	if (rate == 44100 || rate == 48000 || rate == 96000) {
+	if (IS_ERR(priv->extclk)) {
 		/* use internal dco for the supported rates
 		 * defined in kirkwood_i2s_dai */
 		dev_dbg(dai->dev, "%s: dco set rate = %lu\n",