ASoC: simple_card_utils.h: care NULL dai at asoc_simple_debug_dai()

props->xxx_dai might be NULL when DPCM.
This patch cares it for debug.

Fixes: commit 0580dde5 ("ASoC: simple-card-utils: add asoc_simple_debug_info()")
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87o922gw4u.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>