ASoC: wm_adsp: Ensure DSP controls are always persistent

Currently DSP controls are persistent (across DSP On/Off) only
if they were set whilst the DSP is off. This change makes the
controls persistent irrespective of when they are set.

Signed-off-by: Nikesh Oswal <Nikesh.Oswal@wolfsonmicro.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>