drm/amdgpu: fix the clearing wb size

The clearing wb size should be the one that it is assigned.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
1 file changed