ASoC: simple-card: use devm_get_clk_from_child()

Current simple-card-utils is getting clk by of_clk_get(), but didn't call
clk_free(). Now we can use devm_get_clk_from_child() for this purpose.
Let's use it.

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