rtc: allow rtc_set to return an error and use it in cmd_date

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/drivers/rtc/ds1307.c b/drivers/rtc/ds1307.c
index 11fc14f..afc4b78 100644
--- a/drivers/rtc/ds1307.c
+++ b/drivers/rtc/ds1307.c
@@ -128,7 +128,7 @@
 /*
  * Set the RTC
  */
-void rtc_set (struct rtc_time *tmp)
+int rtc_set (struct rtc_time *tmp)
 {
 	DEBUGR ("Set DATE: %4d-%02d-%02d (wday=%d)  TIME: %2d:%02d:%02d\n",
 		tmp->tm_year, tmp->tm_mon, tmp->tm_mday, tmp->tm_wday,
@@ -144,6 +144,8 @@
 	rtc_write (RTC_HR_REG_ADDR, bin2bcd (tmp->tm_hour));
 	rtc_write (RTC_MIN_REG_ADDR, bin2bcd (tmp->tm_min));
 	rtc_write (RTC_SEC_REG_ADDR, bin2bcd (tmp->tm_sec));
+
+	return 0;
 }