drm/amdgpu: fix comment on amdgpu_bo_va

Except for the reference count all other members are protected
by the VM PD being reserved.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -49,9 +49,11 @@ struct amdgpu_bo_va {
 	struct amdgpu_vm_bo_base	base;
 
 	/* protected by bo being reserved */
-	struct dma_fence	        *last_pt_update;
 	unsigned			ref_count;
 
+	/* all other members protected by the VM PD being reserved */
+	struct dma_fence	        *last_pt_update;
+
 	/* mappings for this bo_va */
 	struct list_head		invalids;
 	struct list_head		valids;