drm/amd/powerplay: avoid deadlock on Vega20 swSMU routine

The lock required was already hold by its parent API.
Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/powerplay/amdgpu_smu.c

@@ -2279,13 +2279,9 @@ int smu_set_active_display_count(struct smu_context *smu, uint32_t count)
 {
 	int ret = 0;
 
-	mutex_lock(&smu->mutex);
-
 	if (smu->ppt_funcs->set_active_display_count)
 		ret = smu->ppt_funcs->set_active_display_count(smu, count);
 
-	mutex_unlock(&smu->mutex);
-
 	return ret;
 }