ASoC: soc-pcm: use dpcm_get_be() at dpcm_end_walk_at_be()

dpcm_end_walk_at_be() and dpcm_get_be() are almost same code.
This patch uses dpcm_get_be() from dpcm_end_walk_at_be().

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/87d0adbouh.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>