/proc/acpi/alarm: handle day-of-month wraparound on readback

Fix month wrap issue with readback from /proc/acpi/alarm
This bug has been around *forever*.

  $ echo '2008-12-01 10:36:20' > /proc/acpi/alarm
  $ cat /proc/acpi/alarm
  2008-11-01 10:36:20

Note how the readback above shows the month incorrectly
when the alarm is set in the *next* calendar month.
But with this patch applied, it shows the correct month (12).

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Len Brown <len.brown@intel.com>