ramips: 6.1: dai_dma: drop dma_data->slave_id in mt7620 support patch

ramips: 6.1: dai_dma: drop dma_data->slave_id in mt7620 support patch

Upstream dropped slave_id in dai_dma [0]. So drop it also in the mt7620
support patch.

Fixes errors in the form of:
   sound/soc/ralink/ralink-i2s.c: In function 'ralink_i2s_init_dma_data':
  sound/soc/ralink/ralink-i2s.c:452:17: error: 'struct snd_dmaengine_dai_dma_data' has no member named 'slave_id'
    452 |         dma_data->slave_id = i2s->txdma_req;
        |                 ^~
  sound/soc/ralink/ralink-i2s.c:462:17: error: 'struct snd_dmaengine_dai_dma_data' has no member named 'slave_id'
    462 |         dma_data->slave_id = i2s->rxdma_req;
        |                 ^~

[0] - https://lore.kernel.org/r/20211122222203.4103644-3-arnd@kernel.org

Signed-off-by: Nick Hainke <vincent@systemli.org>