ASoC: wm9713: Use core AC'97 reset helper

Use the new snd_ac97_reset() helper and the reset functionality provided by
snd_soc_new_ac97_codec() to perform the device reset rather than
open-coding it.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>