drm-tests: Use stdout if there is no error

BUG=chrome-os-partner:61504
TEST=graphics_Drm.swrast_test

Change-Id: I633c80b5665161d1d2367adde8fc75cf9cbb8477
Reviewed-on: https://chromium-review.googlesource.com/418541
Commit-Ready: Pratik Vishwakarma <Pratik.Vishwakarma@amd.com>
Tested-by: Pratik Vishwakarma <Pratik.Vishwakarma@amd.com>
Reviewed-by: Zach Reizner <zachr@chromium.org>
1 file changed