ASoC: SOF: mediatek: Fix error code in probe

This should return PTR_ERR() instead of IS_ERR().

Fixes: e0100bfd

 ("ASoC: SOF: mediatek: Add mt8186 ipc support")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/YqmWIK8sTj578OJP@kili
Signed-off-by: Mark Brown <broonie@kernel.org>