ASoC: rsnd: check for zero node count

Most callers of_get_child_count() check that "nr" is non-zero so it
causes a static checker warning when we don't do that here.  This
does not cause a problem or a crash, but having zero SSUIes does not
make sense either so let's add a check.

Addresses-Coverity: ("Unchecked return value")
Fixes: c413983e ("ASoC: rsnd: adjust disabled module")
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210603110315.81146-1-colin.king@canonical.com


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