[PATCH -next] iio: st_accel: Fix unused variable warning

[YueHaibing]

drivers/iio/accel/st_accel_core.c:1005:44: warning:
 mount_matrix_ext_info defined but not used [-Wunused-const-variable=]

Move it to ifdef to mute this warning.

Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
---
 drivers/iio/accel/st_accel_core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/iio/accel/st_accel_core.c b/drivers/iio/accel/st_accel_core.c
index 2e37f8a..bba0717 100644
--- a/drivers/iio/accel/st_accel_core.c
+++ b/drivers/iio/accel/st_accel_core.c
@@ -1002,10 +1002,12 @@ get_mount_matrix(const struct iio_dev *indio_dev,
 	return adata->mount_matrix;
 }
 
+#ifdef CONFIG_ACPI
 static const struct iio_chan_spec_ext_info mount_matrix_ext_info[] = {
 	IIO_MOUNT_MATRIX(IIO_SHARED_BY_ALL, get_mount_matrix),
 	{ },
 };
+#endif
 
 /* Read ST-specific _ONT orientation data from ACPI and generate an
  * appropriate mount matrix.
-- 
2.7.4