alarmtimer: add verification for rtc dev in power_on_alarm_init

Call alarmtimer_get_rtcdev() to get rtcdev instead of using the global
variable rtcdev to avoid the potential risk that rtcdev is not initialized
before using it.

Change-Id: Id186db22849b3667b553f34236a694f9ec6725a7
Signed-off-by: Mao Jinlong <c_jmao@codeaurora.org>
1 file changed