rtc/m48t86: use rtc_valid_tm() to check returned tm

Use rtc_valid_tm() to check the returned struct rtc_time *tm, to avoid
returning a wrong tm value.
Signed-off-by: Wan ZongShun <mcuos.com@gmail.com>
Cc: Paul Gortmaker <p_gortmaker@yahoo.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-m48t86.c

@@ -77,7 +77,7 @@ static int m48t86_rtc_read_time(struct device *dev, struct rtc_time *tm)
 		if (ops->readbyte(M48T86_REG_HOUR) & 0x80)
 			tm->tm_hour += 12;
 
-	return 0;
+	return rtc_valid_tm(tm);
 }
 
 static int m48t86_rtc_set_time(struct device *dev, struct rtc_time *tm)