ASoC: wm_adsp: Only write shutdown controls for active firmwares

The control list may contain shutdown controls for firmwares that are
not currently active, attempting to write this will at best fail. To
avoid this issue we skip any control that is not active.

Fixes: commit f4f0c4c6 ("ASoC: wm_adsp: Signal firmware shutdown
                             through event control")
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>