ASoC: rockchip: ignore 0Hz sysclk

This patch ignores sysclk setting if it is 0Hz.

Some codecs treat 0Hz sysclk as signal of applying no constraints.
This driver does not have such feature but current implementation
outputs 'Failed to set mclk' error message if machine driver sets
0Hz sysclk to this driver.

Signed-off-by: Katsuhiro Suzuki <katsuhiro@katsuster.net>
Link: https://lore.kernel.org/r/20190907174332.19586-1-katsuhiro@katsuster.net


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