sched/topology: Update init_sched_domains() comment

Holding hotplug lock is not a requirement anymore for callers of sched_
init_domains after commit:

  6acce3ef

 ("sched: Remove get_online_cpus() usage")

Update the relative comment preceding init_sched_domains().

Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: cgroups@vger.kernel.org
Cc: lizefan@huawei.com
Link: http://lkml.kernel.org/r/20181219133445.31982-2-juri.lelli@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>