ASoC: rsnd: fixup reset timing of sync convert_rate

Sync convert rate settings should be availabled *after* Playing.
Thus, src->sync should be reset first of init function.
Otherwise, it will set remaining settings when it start playing.
This patch fixes it. Thanks to Yokoyama-san

Reported-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>