ASoC: rockchip: spdif: Handle clk by pm runtime

This patch handle the clk by pm runtime mechanism to simplify
the clk management.

Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>
Link: https://lore.kernel.org/r/1594635960-67855-1-git-send-email-sugar.zhang@rock-chips.com


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