Populate black level gain in blacklevel::prepare(). A copy is made of the gain value in the DebayerParams structure. Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com> Reviewed-by: Milan Zamazal <mzamazal@redhat.com> Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org> Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>