Fix CMOS time error after writing /proc/acpi/alarm

Fix CMOS time error after writing /proc/acpi/alarm

When writing /proc/acpi/alarm in adjust mode, e.g.
        echo "+0000-00-00 00:00:15" >/proc/acpi/alarm
The "century" field should be read and added to "year" field before
writing, otherwise the CMOS time will go back to 2000 years ago, e.g.
        # cat /proc/acpi/alarm
        0008-06-21 11:38:46=20
Then the system time may be reset to the date of manufacture after
rebooting. This patch fixes this issue.

Signed-off-by: Huacai Chen <huacai.chen@intel.com>