ASoC: soc-pcm: tidyup soc_pcm_pointer()'s delay update method

No driver directly updates runtime->delay in .pointer.
This patch cleanups its method.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87zgq4wnkx.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>