[3.34] mpris: Fix LoopStatus getter
According to MPRIS specifications, LoopStatus may be:
- "None" if the playback will stop when there are no more tracks to play. This matches RepeatMode.{NONE,SHUFFLE} in GNOME Music.
- "Track" if the current track will start again from the begining once it has finished playing. This matches RepeatMode.SONG in GNOME Music.
- "Playlist" if the playback loops through a list of tracks. This matches RepeatMode.ALL in GNOME Music.
In shuffle mode, the current LoopStatus getter returns "Playlist" instead of "None".
This issue is fixed by updating the getter to return the correct values.
(cherry picked from commit 04180ba7)