ASoC: wm_adsp: Explicitly set the control access flags in all cases

In the case where the firmware does not tell us the access flags for the
control, we let ALSA select a default (READWRITE). But really we should
be applying the volatile flag in this case, as we will read the control
from the DSP if it is on in this case. This patch explicitly sets the
access flags in all cases.

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