ASoC: rsnd: rename rsnd_src_pcm_new() to rsnd_src_pcm_new_gen2()

rsnd_src_pcm_new() is used only from Gen2. make it clear in function name,
and remove unneeded Gen1 check.

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