drm/amdgpu/swsmu/vangogh: return error if fetching metrics fails

rather than just dropping the error.  Also fixes a set but not
used variable warning.

Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/swsmu/smu11/vangogh_ppt.c

@@ -410,6 +410,8 @@ static int vangogh_get_current_activity_percent(struct smu_context *smu,
 		ret = vangogh_get_smu_metrics_data(smu,
 						  METRICS_AVERAGE_GFXACTIVITY,
 						  value);
+		if (ret)
+			return ret;
 		break;
 	default:
 		dev_err(smu->adev->dev, "Invalid sensor for retrieving clock activity\n");