ASoC: rsnd: remove mismatch explain comment from src.c

Before, src.c cares SRC and SSIU, but now SSIU is cared by ssiu.c by
commit c7f69ab5 ("ASoC: rsnd: use mod base common method on SSIU").
This patch removes mismatched explanation for SRC/SSIU from src.c

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