The ipa::RPi::IpaBase::monoSensor() function doesn't modify the class.
Make it const.
Fixes: 2031e2f290 ("ipa: rpi: Add accessor function for monoSensor_")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>