ASoC: rsnd: dma: add DMA name on .ops

Current rsnd driver is using Audio DMAC (via DMAEngine) and
Audio DMAC peri peri (via original method), and usage of these DMAC
are different. Indicates its naming is useful for debugging.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Keita Kobayashi <keita.kobayashi.ym@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>