drm: Remove slot checks in dp mst topology during commit

This code path is used during commit, and we dont expect things to fail
during the commit stage, so remove this.

Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211025223825.301703-2-lyude@redhat.com