ASoC: rsnd: tidyup direction name on rsnd_dai_connect()

commit 2c6b6a3e ("ASoC: rsnd: use snd_pcm_direction_name()") uses
snd_pcm_direction_name() instead of original method to get string
"Playback" or "Capture". But io->substream might be NULL in this timing.
Let's re-use original method.

Fixes: 2c6b6a3e ("ASoC: rsnd: use snd_pcm_direction_name()")
Reported-by: Thuan Nguyen <thuan.nguyen-hong@banvien.com.vn>
Tested-by: Thuan Nguyen <thuan.nguyen-hong@banvien.com.vn>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Message-ID: <87zfbmwq6v.wl-kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>