stm32f0: fix handling of RTC alarm 24 hour rollover
stm32f0: fix handling of RTC alarm 24 hour rollover

Fix bug in RTC module for stm32f0 in which it doesn't handle the
24 hour rollover appropriately and can cause a watchdog reset
if in deep sleep during rollover.

BUG=chrome-os-partner:36920
BRANCH=samus
TEST=add line to rtc_init()
STM32_RTC_TR = 0x00235952
This initializes RTC clock to 8 seconds before rollover. Using samus
make sure unit is allowed to go to deep sleep (S3/S5 and not charging)
and see that without this CL we watchdog most of the time, and with
this CL we don't watchdog ever.

Change-Id: I3f4b4b1ab7b2be1d4e344477d5eaaa0dc916773a
Signed-off-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/251852
Reviewed-by: Alexandru Stan <1784cbba6d7675b1eba55eaefe41c7672ad9da3b@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,eatbyte/chromium-ec,akappy7/ChromeOS_EC_LED_Diagnostics,md5555/ec,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec,fourier49/BIZ_EC,md5555/ec,md5555/ec,coreboot/chrome-ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec,fourier49/BIZ_EC,eatbyte/chromium-ec,coreboot/chrome-ec,fourier49/BIZ_EC,fourier49/BIZ_EC,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,fourier49/BZ_DEV_EC,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec,fourier49/BZ_DEV_EC,md5555/ec,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BZ_DEV_EC