ASoC: wm_adsp: Mimic legacy behaviour of reading controls when DSP is on

Older firmwares don't specify access flags for the controls,
unfortunately the usage of some of these firmware relies on being able
to read back values from the DSP. The current control code will only do
this for volatile controls. This patch will read the control from the
hardware if no flags are specified and the control is currently
enabled, which should cover these legacy use-cases.

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