ASoC: Fix snd_soc_{new,free}_ac97_codec() locking removal

Commit e3f205a7 ("ASoC: Remove locking in
snd_soc_{new,free}_ac97_codec()") overlooked a unlock on one of the error
paths.

Fixes: e3f205a7 ("ASoC: Remove locking in snd_soc_{new,free}_ac97_codec()")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>