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 <[e-mail]>
Cc: Alessandro Zummo <[e-mail]>
Cc: Alexandre Belloni <[e-mail]>
Signed-off-by: Alexandre Belloni <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/rtc/rtc-mc146818-lib.c

···
 	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;
 	}
 
 	/*
···
 
 	time->tm_mon--;
 
-	return RTC_24H;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(mc146818_get_time);