sched/deadline: Make two functions static

Since commit 06a76fe0 ("sched/deadline: Move DL related code
from sched/core.c to sched/deadline.c"), DL related code moved to
deadline.c.

Make the following two functions static since they're only used in
deadline.c:

	dl_change_utilization()
	init_dl_rq_bw_ratio()

Signed-off-by: Yu Chen <chen.yu@easystack.cn>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200228100329.16927-1-chen.yu@easystack.cn