ASoC: soc-pcm: cleanup cppcheck warning at dpcm_runtime_setup_be_chan()

This patch cleanups below cppcheck warning.

sound/soc/soc-pcm.c:1624:30: style: The scope of the variable 'codec_stream' can be reduced. [variableScope]
  struct snd_soc_pcm_stream *codec_stream;
                             ^

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87o8aozf28.wl-kuninori.morimoto.gx@renesas.com


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