rtc: cmos: Evaluate century appropriate

There's limiting the year to 2069. When setting the rtc year to 2070,
reading it returns 1970. Evaluate century starting from 19 to count the
correct year.

$ sudo date -s 20700106
Mon 06 Jan 2070 12:00:00 AM CST
$ sudo hwclock -w
$ sudo hwclock -r
1970-01-06 12:00:49.604968+08:00

Fixes: 2a4daad ("rtc: cmos: ignore bogus century byte")

Signed-off-by: Riwen Lu <luriwen@kylinos.cn>
Acked-by: Eric Wong <e@80x24.org>
Reviewed-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220106084609.1223688-1-luriwen@kylinos.cn

Author: Riwen Lu

drivers/rtc/rtc-mc146818-lib.c

@@ -159,7 +159,7 @@ int mc146818_get_time(struct rtc_time *time)
 #endif
 
 #ifdef CONFIG_ACPI
-	if (p.century > 20)
+	if (p.century > 19)
 		time->tm_year += (p.century - 19) * 100;
 #endif