debug: thread_analyzer: fix incorrect k_thread_foreach_unlocked argument

Fix the second k_thread_foreach_unlocked argument, it's supposed to be
an instance of ta_cb_user_data as that's what's it casted back to in
thread_analyze_cb. Current code results in an exception and crash for
single core applications.

This is a regression introduced in 1b6e0f64.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>