ASoC: omap: n810: Convert to clk_prepare_enable/clk_disable_unprepare

N810 audio driver has stopped working at some point. Probably when
OMAP2 was converted to common clock framework since now call to clk_enable
dumps the stack trace in drivers/clk/clk.c: __clk_enable() due
clk->prepare_count is zero.

Fix this by converting clk_enable/_disable calls to those that take care
of clock prepare/unprepare.

I'm not queueing this to linux-stable since OMAP2 common clock framework
conversion in commit ed1ebc49 ("ARM: OMAP2: clock: Convert to common clk")
happened before N810 was really usable in mainline and user base for N810 is
anyway small. Potential linux-stable candidates are only those after
commit 3d3a6d18

 ("watchdog: introduce retu_wdt driver").

Signed-off-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Signed-off-by: Mark Brown <broonie@linaro.org>