rtc: refine rtc_timer_do_work() to consider other set alarm failures

rtc: refine rtc_timer_do_work() to consider other set alarm failures

rtc_timer_do_work() only judges -ETIME failure of__rtc_set_alarm(), but
doesn't handle other failures like -EIO, -EBUSY, etc.

If there is a failure other than -ETIME, the next rtc_timer will stay in
the timerqueue.  Then later rtc_timers will be enqueued directly because
they have a later expires time, so the alarm irq will never be programmed.

When such failures happen, this patch will retry __rtc_set_alarm(), if
still can't program the alarm time, it will remove current rtc_timer from
timerqueue and fetch next one, thus preventing it from affecting other rtc
timers.

Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Arnd Bergmann <arnd.bergmann@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>