drm/dp_mst: Get rid of old comment in drm_atomic_get_mst_topology_state docs

We don't actually care about connection_mutex here anymore, so let's get
rid of the comment mentioning it in this function's kdocs.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Wayne Lin <Wayne.Lin@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220602201757.30431-4-lyude@redhat.com

drivers/gpu/drm/display/drm_dp_mst_topology.c

@@ -5456,8 +5456,7 @@ EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
  *
  * This function wraps drm_atomic_get_priv_obj_state() passing in the MST atomic
  * state vtable so that the private object state returned is that of a MST
- * topology object. Also, drm_atomic_get_private_obj_state() expects the caller
- * to care of the locking, so warn if don't hold the connection_mutex.
+ * topology object.
  *
  * RETURNS:
  *