drm/radeon: drop confusing message about backlight control

The message is harmless and confusing.  On PX systems,
there is one ATIF method, but potentially multiple GPUs
leading to an error on the GPU with no backlight control.

Bug: https://bugzilla.kernel.org/show_bug.cgi?id=115011
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Hans de Goede <jwrdegoede@fedoraproject.org>

drivers/gpu/drm/radeon/radeon_acpi.c

@@ -741,13 +741,6 @@ int radeon_acpi_init(struct radeon_device *rdev)
 		}
 
 		atif->encoder_for_bl = target;
-		if (!target) {
-			/* Brightness change notification is enabled, but we
-			 * didn't find a backlight controller, this should
-			 * never happen.
-			 */
-			DRM_ERROR("Cannot find a backlight controller\n");
-		}
 	}
 
 	if (atif->functions.sbios_requests && !atif->functions.system_params) {