ucm: include - fix compound_merge for arrays
ucm: include - fix compound_merge for arrays

There is a case where the original array has already new indexes
(the merged array is placed before the original nodes).

Set the temporary index string identifiers to unique strings.

Signed-off-by: Jaroslav Kysela <72edd5e1a572f82f059ccbb83c92b74d6cb051ff@perex.cz>

alsa-project/alsa-lib,tiwai/alsa-lib,tiwai/alsa-lib,takaswie/alsa-lib,tiwai/alsa-lib,takaswie/alsa-lib,takaswie/alsa-lib,alsa-project/alsa-lib,takaswie/alsa-lib,alsa-project/alsa-lib,alsa-project/alsa-lib,tiwai/alsa-lib,takaswie/alsa-lib