test/py: fix spawn.expect multiple match handling

Multiple patterns may be passed to spawn.expect(). The pattern which
matches at the earliest position should be designated as the match. This
aspect works correctly. When multiple patterns match at the same position,
priority should be given the the earliest entry in the list of patterns.
This aspect does not work correctly. This patch fixes it.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>