ASoC: Add missing gpio_free(S3C64XX_GPK(12)) in smartq_exit()

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Jassi Brar <jassi.brar@samsung.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>