drm/dp_mst: make build_clear_payload_id_table return void

Nothing uses the always-0 return value.

Signed-off-by: Maya Rashish <coypu@sdf.org>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200321222959.GA1053@SDF.ORG