[PATCH v2] iio: adc: ad_sigma_delta: Fix use of uninitialized status_pos

[Purva Yeshi <purvayeshi550@gmail.com>]

Fix Smatch-detected issue:
drivers/iio/adc/ad_sigma_delta.c:604 ad_sd_trigger_handler() error:
uninitialized symbol 'status_pos'.

The variable `status_pos` was only initialized in specific switch cases
(1, 2, 3, 4), which could leave it uninitialized if `reg_size` had an
unexpected value.

Fix by adding a default case to the switch block to catch unexpected
values of `reg_size`. Use `dev_err_ratelimited()` for error logging and
`goto irq_handled` instead of returning early.

Signed-off-by: Purva Yeshi <purvayeshi550@gmail.com>
---
V1 - https://lore.kernel.org/all/20250409200151.201327-1-purvayeshi550@gmail.com/
V2 - Moved the reg_size validation inside the switch statement using a default case,
replaced dev_err() with dev_err_ratelimited(), and replaced return IRQ_HANDLED
with goto irq_handled;

 drivers/iio/adc/ad_sigma_delta.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
index 6c37f8e21120..4c5f8d29a559 100644
--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -587,6 +587,10 @@ static irqreturn_t ad_sd_trigger_handler(int irq, void *p)
 		 * byte set to zero. */
 		ad_sd_read_reg_raw(sigma_delta, data_reg, transfer_size, &data[1]);
 		break;
+
+	default:
+		dev_err_ratelimited(&indio_dev->dev, "Unsupported reg_size: %u\n", reg_size);
+		goto irq_handled;
 	}
 
 	/*
-- 
2.34.1