drm/radeon: move bl encoder assignment into bl init

So that the bl encoder will be null if the GPU does not
control the backlight.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/radeon/radeon_encoders.c

@@ -194,7 +194,6 @@ static void radeon_encoder_add_backlight(struct radeon_encoder *radeon_encoder,
 			radeon_atom_backlight_init(radeon_encoder, connector);
 		else
 			radeon_legacy_backlight_init(radeon_encoder, connector);
-		rdev->mode_info.bl_encoder = radeon_encoder;
 	}
 }