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/board/mousse/m48t59y.c b/board/mousse/m48t59y.c
index 2c1e6cf..beb26fe 100644
--- a/board/mousse/m48t59y.c
+++ b/board/mousse/m48t59y.c
@@ -299,8 +299,7 @@
 	return 0;
 }
 
-void
-rtc_set( struct rtc_time *tmp )
+int rtc_set( struct rtc_time *tmp )
 {
 	m48_tod_set(tmp->tm_year,		/* 1980-2079 */
 		    tmp->tm_mon,		/* 01-12 */
@@ -315,6 +314,7 @@
 		tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
 #endif
 
+	return 0;
 }
 
 void