ASoC: rsnd: rename rsnd_enable_sync_convert() to rsnd_src_sync_is_enabled()

rsnd_enable_sync_convert() is for checking, not for setting.
In order to avoid confusion, this patch renamed it to
rsnd_src_sync_is_enabled()

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