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: NHuacai Chen <huacai.chen@intel.com>
Acked-by: NPavel Machek <pavel@suse.cz>
Acked-by: NZhao Yakui <yakui.zhao@intel.com>
Acked-by: NAlessandro Zummo <a.zummo@towertech.it>
Acked-by: NLen Brown <lenb@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/acpi/sleep/proc.c

@@ -315,8 +315,11 @@ acpi_system_write_alarm(struct file *file,
 		cmos_bcd_write(day, acpi_gbl_FADT.day_alarm, rtc_control);
 	if (acpi_gbl_FADT.month_alarm)
 		cmos_bcd_write(mo, acpi_gbl_FADT.month_alarm, rtc_control);
-	if (acpi_gbl_FADT.century)
+	if (acpi_gbl_FADT.century) {
+		if (adjust)
+			yr += cmos_bcd_read(acpi_gbl_FADT.century, rtc_control) * 100;
 		cmos_bcd_write(yr / 100, acpi_gbl_FADT.century, rtc_control);
+	}
 	/* enable the rtc alarm interrupt */
 	rtc_control |= RTC_AIE;
 	CMOS_WRITE(rtc_control, RTC_CONTROL);