Fix: change expected number of event for test uid

With UST commit d970f72ef97cd5f1e5e0152ce48a4c6b28eccfb2, enabling the
same events in two different channels make write them two times instead
of once.

This commit changes the number of expected events in one test for per
UID buffers.

Signed-off-by: David Goulet <dgoulet@efficios.com>