ASoC: Declare 2 channels for WM8974

The device is a mono device but it can read two channel data and
many I2S controllers only understand 2 channels.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/wm8974.c

@@ -582,13 +582,13 @@ struct snd_soc_dai wm8974_dai = {
 	.playback = {
 		.stream_name = "Playback",
 		.channels_min = 1,
-		.channels_max = 1,
+		.channels_max = 2,   /* Only 1 channel of data */
 		.rates = WM8974_RATES,
 		.formats = WM8974_FORMATS,},
 	.capture = {
 		.stream_name = "Capture",
 		.channels_min = 1,
-		.channels_max = 1,
+		.channels_max = 2,   /* Only 1 channel of data */
 		.rates = WM8974_RATES,
 		.formats = WM8974_FORMATS,},
 	.ops = &wm8974_ops,