drm/amdgpu: Don't take dev->struct_mutex in bo_force_delete

It really doesn't protect anything which doesn't have other locks
already. Also this is run from driver unload code so not much need for
locks anyway.

Same changes as for radeon really.

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -466,7 +466,6 @@ void amdgpu_bo_force_delete(struct amdgpu_device *adev)
 	}
 	dev_err(adev->dev, "Userspace still has active objects !\n");
 	list_for_each_entry_safe(bo, n, &adev->gem.objects, list) {
-		mutex_lock(&adev->ddev->struct_mutex);
 		dev_err(adev->dev, "%p %p %lu %lu force free\n",
 			&bo->gem_base, bo, (unsigned long)bo->gem_base.size,
 			*((unsigned long *)&bo->gem_base.refcount));
@@ -474,8 +473,7 @@ void amdgpu_bo_force_delete(struct amdgpu_device *adev)
 		list_del_init(&bo->list);
 		mutex_unlock(&bo->adev->gem.mutex);
 		/* this should unref the ttm bo */
-		drm_gem_object_unreference(&bo->gem_base);
-		mutex_unlock(&adev->ddev->struct_mutex);
+		drm_gem_object_unreference_unlocked(&bo->gem_base);
 	}
 }