ASoC: rockchip: namespace rockchip i2s module name

Change the rockchip i2s object name (and thus module name) from the
rather generic snd-soc-i2s to the more specific snd-soc-rockchip-i2s

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: Mark Brown <broonie@kernel.org>