wm_adsp_write_ctl() must hold the pwr_lock mutex when calling
cs_dsp_get_ctl().
This was previously partially fixed by commit 781118bc2fc1
("ASoC: wm_adsp: Fix missing locking in wm_adsp_[read|write]_ctl()")
but this only put locking around the call to cs_dsp_coeff_write_ctrl(),
missing the call to cs_dsp_get_ctl().