iio: imu: lsm6dsx: Fix mount matrix retrieval

The function lsm6dsx_get_acpi_mount_matrix should return an error when ACPI
support is not enabled to allow executing iio_read_mount_matrix in the
probe function.

Fixes: dc3d25f2 ("iio: imu: lsm6dsx: Add ACPI mount matrix retrieval")
Signed-off-by: Alejandro Tafalla <atafalla@dnyon.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/20230714153132.27265-1-atafalla@dnyon.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c

@@ -2687,7 +2687,7 @@ static int lsm6dsx_get_acpi_mount_matrix(struct device *dev,
 static int lsm6dsx_get_acpi_mount_matrix(struct device *dev,
 					  struct iio_mount_matrix *orientation)
 {
-	return false;
+	return -EOPNOTSUPP;
 }
 
 #endif