ASoC: wm8900: Fix the wrong number of enum items

wm8900 codec driver has a few places wrongly defining the number of
enum items.

Use SOC_ENUM_SINGLE_DECL() macro and they are automatically fixed.

Acked-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@linaro.org>