glbench: specify drm device to use

Waffle defaults to opening a render node, but we need a regular drm
device in order to determine the screen size.

BUG=chromium:413080
TEST=test_that -b samus -i trybot-samus-paladin/R42-6738.0.0-b154 :lab: graphics_GLBench

Change-Id: I57e984fc16456a4115ee032f74125a5761393db4
Reviewed-on: https://chromium-review.googlesource.com/244461
Reviewed-by: Ilja Friedel <ihf@chromium.org>
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>
Tested-by: Frank Henigman <fjhenigman@chromium.org>
1 file changed