ASoC: simple-card: tidyup mclk-fs of_property_read_u32() usage

of_property_read_u32() do nothing in error case.
Let's tidyup useless usage.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>