ASoC: rsnd: tidyup src->convert_rate reset timing

Current src->convert_rate will be set on .hw_param, and
be reset on .quit timing.
But, .hw_param will not be called again if user did Ctrl-Z + fg.
It should be reset on initial of .hw_param to keep its value.
Here, ctu.c already do this.
This patch solves this issue, other wise, MIXed sound will be
strange if user did like below.

	> aplay -D plughw:0,0 sound_44100.wav &
	> aplay -D plughw:0,1 sound_96000.wav
	> Ctrl-Z
	> fg # 96kHz will be played as 44.1kHz

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