rtc: fix CMOS time error after writing /proc/acpi/alarm

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 <[email protected]>
Acked-by: Pavel Machek <[email protected]>
Acked-by: Zhao Yakui <[email protected]>
Acked-by: Alessandro Zummo <[email protected]>
Acked-by: Len Brown <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>