drm/amdgpu/display: make backlight setting failure messages debug

Avoid spamming the log.  The backlight controller on DCN chips
gets powered down when the display is off, so if you attempt to
set the backlight level when the display is off, you'll get this
message.  This isn't a problem as we cache the requested backlight
level if it's adjusted when the display is off and set it again
during modeset.
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: nicholas.choi@amd.com
Cc: harry.wentland@amd.com

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -3506,7 +3506,7 @@ static int amdgpu_dm_backlight_set_level(struct amdgpu_display_manager *dm,
 			rc = dc_link_set_backlight_level_nits(link[i], true, brightness[i],
 				AUX_BL_DEFAULT_TRANSITION_TIME_MS);
 			if (!rc) {
-				DRM_ERROR("DM: Failed to update backlight via AUX on eDP[%d]\n", i);
+				DRM_DEBUG("DM: Failed to update backlight via AUX on eDP[%d]\n", i);
 				break;
 			}
 		}
@@ -3514,7 +3514,7 @@ static int amdgpu_dm_backlight_set_level(struct amdgpu_display_manager *dm,
 		for (i = 0; i < dm->num_of_edps; i++) {
 			rc = dc_link_set_backlight_level(dm->backlight_link[i], brightness[i], 0);
 			if (!rc) {
-				DRM_ERROR("DM: Failed to update backlight on eDP[%d]\n", i);
+				DRM_DEBUG("DM: Failed to update backlight on eDP[%d]\n", i);
 				break;
 			}
 		}