test: Fix missing livetree test runs

At present the live tree tests are not run on sandbox. This bug is in two
parts, with a duplicate flag value and incorrect logic in the test runner.
This was not noticed because the bug was fixed in a later commit and does
not cause test failures.

Fix this.

Fixes: 7b1dfc9fd7e ("dm: core: Prepare for updating the device tree with ofnode")

Signed-off-by: Simon Glass <sjg@chromium.org>
3 files changed