staging: tidspbridge: use prepare/unprepare on dsp clocks

This solves runtime failures while trying to enable WDT3 related
functionality on firmware load, however it does affect other clocks
controlled by the driver. Seen on 3.8-rc1.

CCF provides clk_prepare and clk_unprepare for enable and disable
operations respectively, this needs to be called in the correct
order while handling clocks.

Code path to enable/disable dsp clocks can still be reached from an
atomic context, hence we can't use clk_prepare_enable and
clk_disable_unprepare yet.

Signed-off-by: Omar Ramirez Luna <omar.ramirez@copitl.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>