After commit 571c0536 ("drm/amdgpu: switch sdma buffer function
tear down to a helper"), the variable 'ring' is not used anymore, it
can be removed.
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>