ASoC: amd: raven: acp3x-i2s: fix 'set but not used' warning

Fix W=1 warning. the card variable is useless here

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200702164433.162815-5-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>