ASoC: Limit WM8731 to symmetric rates

While the hardware is capable of some limited asynmmetric modes the
driver does not currently support those modes so tell applications
that only symmetric rates are available.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/wm8731.c

@@ -464,6 +464,7 @@ struct snd_soc_dai wm8731_dai = {
 		.rates = WM8731_RATES,
 		.formats = WM8731_FORMATS,},
 	.ops = &wm8731_dai_ops,
+	.symmetric_rates = 1,
 };
 EXPORT_SYMBOL_GPL(wm8731_dai);