ASoC: simple_card_utils: add EXPORT_SYMBOL_GPL() for asoc_simple_card_clk_xxx()

commit 891caea4 ("ASoC: simple_card_utils:
add asoc_simple_card_clk_xxx()") added new asoc_simple_card_clk_xxx(),
but, it didn't have EXPORT_SYMBOL_GPL().
This patch adds it. Otherwise, we will get below error

ERROR: "asoc_simple_card_clk_enable" [sound/soc/generic/snd-soc-simple-scu-card.ko] undefined!
ERROR: "asoc_simple_card_clk_disable" [sound/soc/generic/snd-soc-simple-scu-card.ko] undefined!
ERROR: "asoc_simple_card_clk_enable" [sound/soc/generic/snd-soc-simple-card.ko] undefined!
ERROR: "asoc_simple_card_clk_disable" [sound/soc/generic/snd-soc-simple-card.ko] undefined!
ERROR: "asoc_simple_card_clk_enable" [sound/soc/generic/snd-soc-audio-graph-scu-card.ko] undefined!
ERROR: "asoc_simple_card_clk_disable" [sound/soc/generic/snd-soc-audio-graph-scu-card.ko] undefined!
ERROR: "asoc_simple_card_clk_enable" [sound/soc/generic/snd-soc-audio-graph-card.ko] undefined!
ERROR: "asoc_simple_card_clk_disable" [sound/soc/generic/snd-soc-audio-graph-card.ko] undefined!

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