virsh-snapshot: Use 'virshSnapshotNameCompleter' for '--from' of 'snapshot-list'

When listing a snapshot tree, the '--from' option takes a name of a
snapshot to limit the subset. Use virshSnapshotNameCompleter as
completer for the option.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

tools/virsh-snapshot.c

@@ -1411,6 +1411,7 @@ static const vshCmdOptDef opts_snapshot_list[] = {
     },
     {.name = "from",
      .type = VSH_OT_STRING,
+     .completer = virshSnapshotNameCompleter,
      .help = N_("limit list to children of given snapshot")
     },
     VIRSH_COMMON_OPT_CURRENT(N_("limit list to children of current snapshot")),