ASoC: SDCA: Add flag for unused IRQs

Zero is a valid SDCA IRQ interrupt position so add a special value to
indicate that the IRQ is not used.

Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.dev>
Link: https://patch.msgid.link/20250624122844.2761627-6-ckeepax@opensource.cirrus.com


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