iio: magnetometer: rm3100-core: make use of iio_get_masklength()

Use iio_get_masklength() to access '.masklength' so it can be annotated
as __private when there are no more direct users of it.
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240718-dev-iio-masklength-private2-v1-18-8e12cd042906@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/magnetometer/rm3100-core.c

@@ -464,7 +464,7 @@ static irqreturn_t rm3100_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	unsigned long scan_mask = *indio_dev->active_scan_mask;
-	unsigned int mask_len = indio_dev->masklength;
+	unsigned int mask_len = iio_get_masklength(indio_dev);
 	struct rm3100_data *data = iio_priv(indio_dev);
 	struct regmap *regmap = data->regmap;
 	int ret, i, bit;