USB-audio driver puts SNDRV_CHMAP_SL and _SR as left and right
surround channels for UAC1 channel map, respectively. But they should
have been SNDRV_CHMAP_RL and _RR; the current value *_SL and _SR are
rather "side" channels, not "surround". I guess I took those
mistakenly when I read the spec mentioning "surround left".
This patch corrects those entries to be the right channels.