ASoC: ak4642: don't have .use_pmdown_time

snd_soc_runtime_ignore_pmdown_time() returns "ignore pmdown time"
decision. Then, it collects each component driver's .use_pmdown_time
settings by using AND operation.
But, ak4613 has no reason to ignore/use pmdown time.
Thus, It should has use_pmdown_time=0, it means it doesn't have
decision right of "ignore pmdown time".

Otherwise, ak4642 paired driver's pmdown_time settings doesn't
have meaning. In other words, "ignore pmdown time" is determined
irrespective of the value of paired driver's settings
(= ignore will be 0 by ak4642).

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