ASoC: SOF: sof-acpi-dev: fix 'defined but unused' warning

Fix W=1 warning

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200701183913.83455-1-pierre-louis.bossart@linux.intel.com


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