ASoC: wm_adsp: Don't generate kcontrols without READ flags

ASoC: wm_adsp: Don't generate kcontrols without READ flags

User space always expects to be able to read ALSA controls, so ensure
no kcontrols are generated without an appropriate READ flag. In the case
of a read of such a control zeros will be returned.

Signed-off-by: Stuart Henderson <stuarth@opensource.cirrus.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20191002084240.21589-1-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>