ASoC: wm8804: Drop duplicate const

SOC_ENUM_SINGLE_DECL() already includes a const, drop the extra const.
Fixes the following sparse warning:

	sound/soc/codecs/wm8804.c:101:14: warning: duplicate const
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wm8804.c

@@ -98,7 +98,7 @@ WM8804_REGULATOR_EVENT(0)
 WM8804_REGULATOR_EVENT(1)
 
 static const char *txsrc_text[] = { "S/PDIF RX", "AIF" };
-static const SOC_ENUM_SINGLE_DECL(txsrc, WM8804_SPDTX4, 6, txsrc_text);
+static SOC_ENUM_SINGLE_DECL(txsrc, WM8804_SPDTX4, 6, txsrc_text);
 
 static const struct snd_kcontrol_new wm8804_tx_source_mux[] = {
 	SOC_DAPM_ENUM_EXT("Input Source", txsrc,