rtc: 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
Then the system time may be reset to the date of manufacture after
rebooting. This patch fixed this issue.

Signed-off-by: Huacai Chen <huacai.chen@intel.com>
Acked-by: Pavel Machek <pavel@suse.cz>
Acked-by: Zhao Yakui <yakui.zhao@intel.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Acked-by: Len Brown <lenb@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>