sched_ext: INIT_LIST_HEAD() &sch->all in scx_alloc_and_add_sched()

sched_ext: INIT_LIST_HEAD() &sch->all in scx_alloc_and_add_sched()

On scx_link_sched() error paths (parent disabled, hash insert failure),
&sch->all is never added to scx_sched_all. The cleanup path runs
scx_unlink_sched() unconditionally, which calls list_del_rcu(&sch->all) on a
list_head that was never initialized triggering a corruption warning.

Initialize &sch->all.

Fixes: 54be8de4236a ("sched_ext: Factor out scx_link_sched() and scx_unlink_sched()")
Signed-off-by: Tejun Heo <tj@kernel.org>