rtc-at32ap700x: fix bug in at32_rtc_readalarm()

alarm->pending indicates whether there's an alarm that has actually been
triggered, not whether we're waiting for it.  alarm->enabled indicates
that.

Also add missing locking around reading the RTC registers.

Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>