ASoC: wm9712: Remove ac97_read/ac97_write wrappers

Since the regmap conversion ac97_read/ac97_write are just simple wrappers
around snd_soc_read/snd_soc_write. Use those instead directly and remove
the wrappers. Also use snd_soc_update_bits() were appropriate.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Tested-by: Marek Vasut <marex@denx.de>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>