mm/damon/sysfs: use the wrapper directly to check if the kdamond is running

We can use the 'damon_sysfs_kdamond_running()' wrapper directly to check
if the kdamond is running in 'damon_sysfs_turn_damon_on()'.

Link: https://lkml.kernel.org/r/1662995513-24489-1-git-send-email-kaixuxia@tencent.com


Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>