ASoC: wm8995: Use SOC_ENUM_SINGLE_VIRT_DECL()

For the upcoming consolidation for MUXs and virtual MUXs we need to mark virtual
enums as such.
Signed-off-by: NLars-Peter Clausen <lars@metafoo.de>
Acked-by: NCharles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

sound/soc/codecs/wm8995.c

@@ -882,7 +882,7 @@ static const char *adc_mux_text[] = {
 	"DMIC",
 };
 
-static const SOC_ENUM_SINGLE_DECL(adc_enum, 0, 0, adc_mux_text);
+static SOC_ENUM_SINGLE_VIRT_DECL(adc_enum, adc_mux_text);
 
 static const struct snd_kcontrol_new adcl_mux =
 	SOC_DAPM_ENUM_VIRT("ADCL Mux", adc_enum);