ASoC: rsnd: fixup clock start checker

commit 4d230d12 ("ASoC: rsnd: fixup not to call clk_get/set under
non-atomic") fixuped clock start timing. But it exchanged clock start
checker from ssi->usrcnt to ssi->rate.

Current rsnd_ssi_master_clk_start() is called from .prepare,
but some player (for example GStreamer) might calls it many times.
In such case, the checker might returns error even though it was not
error. It should check ssi->usrcnt instead of ssi->rate.
This patch fixup it. Without this patch, GStreamer can't switch
48kHz / 44.1kHz.

Reported-by: Yusuke Goda <yusuke.goda.sx@renesas.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Yusuke Goda <yusuke.goda.sx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>