perf thread: Ensure comm_lock held for comm_list

Add thread safety annotations for comm_list and add locking for two
instances where the list is accessed without the lock held (in
contradiction to ____thread__set_comm()).

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250529192206.971199-1-irogers@google.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>