ASoC: samsung: s3c24xx-i2s: Move to clk_prepare_enable/clk_disable_unprepare

Use clk_prepare_enable/clk_disable_unprepare to make the driver
work properly with common clock framework.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>