ASoC: SDCA: Fix return value in detected_mode_handler()

The detected mode IRQ handler should return an irqreturn_t not a regular
error code. Correct the return value in detected_mode_handler().

Fixes: b9ab3b61 ("ASoC: SDCA: Add some initial IRQ handlers")
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Message-ID: <20250820163717.1095846-3-ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>