ASoC: wm8994: Move DCS done IRQ request later

once code return from request_threaded_irq, irq was setup enabled by
default, but completion var dcs_done not got initialized yet, if then a
dcs done irq was raised, system will got hung as the sync mechanism is
invalid now.

so this patch move dcs done irq request to the end of initialization
of completion.

Signed-off-by: wang, biao <biao.wang@intel.com>
Signed-off-by: Zhang, Di <di.zhang@intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>