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/ds164x.c b/drivers/rtc/ds164x.c
index c621a9e..00494b3 100644
--- a/drivers/rtc/ds164x.c
+++ b/drivers/rtc/ds164x.c
@@ -119,7 +119,7 @@
 	return 0;
 }
 
-void rtc_set( struct rtc_time *tmp )
+int rtc_set( struct rtc_time *tmp )
 {
 	uchar reg_a;
 
@@ -145,6 +145,8 @@
 
 	/* unlock clock registers after read */
 	rtc_write( RTC_CONTROLA, ( reg_a  & ~RTC_CA_WRITE ));
+
+	return 0;
 }
 
 void rtc_reset (void)