drm/amdgpu: add the lost mutex_init back

Initialize notifier_lock.

Bug: https://gitlab.freedesktop.org/drm/amd/issues/1016Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

@@ -2848,6 +2848,7 @@ int amdgpu_device_init(struct amdgpu_device *adev,
 	hash_init(adev->mn_hash);
 	mutex_init(&adev->lock_reset);
 	mutex_init(&adev->psp.mutex);
+	mutex_init(&adev->notifier_lock);
 
 	r = amdgpu_device_check_arguments(adev);
 	if (r)