ASoC: sh: siu_pcm: remove unused variable

ASoC: sh: siu_pcm: remove unused variable

cppcheck warning:

sound/soc/sh/siu_pcm.c:225:8: style: Variable 'virt' is assigned a
value that is never used. [unreadVariable]

  virt = PERIOD_OFFSET(rt->dma_area,
       ^

It's not clear what this variable was needed for, remove it.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210219231635.5749-9-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>