watchdog: fix watchdog get lefttime error [1/1]

watchdog: fix watchdog get lefttime error [1/1]

PD#SWPL-6937

Problem:
1.get lefttime error by 'cat sys/class/watchdog/watchdog0/timeleft' cmd.
2.if DTS is configured to feed watchdog by Android, the system will
restart automatically after wake up.

Solution:
1.modify the code to get time.
2.when the system wakes up, first judge whether the watchdog runs,
and then decide whether to start the watchdog.

Verify:
test pass on u200

Change-Id: If64888ffdd5651e8cfcace5ea0d0da31641bb397
Signed-off-by: Yingyuan Zhu <yingyuan.zhu@amlogic.com>