drivers/rtc/rtc-rs5c348.c: fix hour decoding in 12-hour mode

Correct the offset by subtracting 20 from tm_hour before taking the
modulo 12.

[ "Why 20?" I hear you ask. Or at least I did.

  Here's the reason why: RS5C348_BIT_PM is 32, and is - stupidly -
  included in the RS5C348_HOURS_MASK define.  So it's really subtracting
  out that bit to get "hour+12".  But then because it does things modulo
  12, it needs to add the 12 in again afterwards anyway.

  This code is confused.  It would be much clearer if RS5C348_HOURS_MASK
  just didn't include the RS5C348_BIT_PM bit at all, then it wouldn't
  need to do the silly subtract either.

  Whatever. It's all just math, the end result is the same.   - Linus ]
Reported-by: James Nute <newten82@gmail.com>
Tested-by: James Nute <newten82@gmail.com>
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-rs5c348.c

@@ -122,9 +122,12 @@ rs5c348_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	tm->tm_min = bcd2bin(rxbuf[RS5C348_REG_MINS] & RS5C348_MINS_MASK);
 	tm->tm_hour = bcd2bin(rxbuf[RS5C348_REG_HOURS] & RS5C348_HOURS_MASK);
 	if (!pdata->rtc_24h) {
-		tm->tm_hour %= 12;
-		if (rxbuf[RS5C348_REG_HOURS] & RS5C348_BIT_PM)
+		if (rxbuf[RS5C348_REG_HOURS] & RS5C348_BIT_PM) {
+			tm->tm_hour -= 20;
+			tm->tm_hour %= 12;
 			tm->tm_hour += 12;
+		} else
+			tm->tm_hour %= 12;
 	}
 	tm->tm_wday = bcd2bin(rxbuf[RS5C348_REG_WDAY] & RS5C348_WDAY_MASK);
 	tm->tm_mday = bcd2bin(rxbuf[RS5C348_REG_DAY] & RS5C348_DAY_MASK);