ASoC: rsnd: rename rsnd_dma_init() to rsnd_dma_attach()

Renesas sound needs many devices
(SSI/SSIU/SRC/CTU/MIX/DVC/CMD/AudioDMAC/AudioDMACpp).
SSI/SRC/CTU/MIX/DVC are implemented as module.
SSI parent, SSIU are implemented as part of SSI
CMD is implemented as part of CTU/MIX/DVC
AudioDMAC/AudioDMACpp are implemented as part of SSI/SRC
It is nice sense that these all devices are implemented as mod.

DMA will be implemented as module. Then each rsnd_dma_ops will be
rsnd_mod_ops. But current rsnd_dma_ops::init means "DMA attach".
This patch removes .init from rsnd_dma_ops, and renames
rsnd_dma_init() to rsnd_dma_attach()

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>