rtc: mc146818-lib: change return values of mc146818_get_time()

No function is checking mc146818_get_time() return values yet, so
correct them to make them more customary.
Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211210200131.153887-3-mat.jonczyk@o2.pl

drivers/rtc/rtc-mc146818-lib.c

@@ -25,7 +25,7 @@ unsigned int mc146818_get_time(struct rtc_time *time)
 	if (WARN_ON_ONCE((CMOS_READ(RTC_VALID) & 0x40) != 0)) {
 		spin_unlock_irqrestore(&rtc_lock, flags);
 		memset(time, 0xff, sizeof(*time));
-		return 0;
+		return -EIO;
 	}
 
 	/*
@@ -116,7 +116,7 @@ unsigned int mc146818_get_time(struct rtc_time *time)
 
 	time->tm_mon--;
 
-	return RTC_24H;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(mc146818_get_time);