drm/amdgpu: remove unused variable from struct amdgpu_bo

Fixes: 62914a99 ("drm/amdgpu: Use mmu_interval_insert instead of hmm_mirror")
Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -100,7 +100,6 @@ struct amdgpu_bo {
 	struct amdgpu_bo		*parent;
 	struct amdgpu_bo		*shadow;
 
-	struct amdgpu_mn		*mn;
 
 
 #ifdef CONFIG_MMU_NOTIFIER