ASoC: ac97: don't call snd_soc_new_ac97_codec at probe

It is not needed since snd_ac97_mixer() will create a new ac97 object for us.
Removing the call also fixes a memory leak since codec->ac97 is set to NULL at
the beginning of snd_ac97_mixer().

Signed-off-by: Mika Westerberg <mika.westerberg@iki.fi>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>