Parallel module loading: Fix typo and simplify logic

Remove redundant `find()` call as `insert()` performs an internal search and use `load_modules_parallel` directly for all mode selection.

Bug: 402263126
Change-Id: Ib87d45843fe34df41eee33fdc72179c964061c73
Signed-off-by: Chungkai Mei <chungkai@google.com>