ASoC: wm_adsp: Add locking to wm_adsp2_bus_error

[ Upstream commit a2225a6d155fcb247fe4c6d87f7c91807462966d ]

Best to lock across handling the bus error to ensure the DSP doesn't
change power state as we are reading the status registers.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>