iio: avoid shadowing of variable name in to_iio_dev_opaque()

indio_dev was both the macro input parameter and the field name
in this macro.  That causes trouble if the instance of
struct iio_dev passed in is not called indio_dev.

Whilst a fix of sorts, no need to backport as it seems we never
hit this previously due to some very consistent naming in IIO.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20210426174911.397061-3-jic23@kernel.org

include/linux/iio/iio-opaque.h

@@ -48,7 +48,7 @@ struct iio_dev_opaque {
 #endif
 };
 
-#define to_iio_dev_opaque(indio_dev)		\
-	container_of(indio_dev, struct iio_dev_opaque, indio_dev)
+#define to_iio_dev_opaque(_indio_dev)		\
+	container_of((_indio_dev), struct iio_dev_opaque, indio_dev)
 
 #endif