LWMON5: POST RTC fix

Modify the RTC API to provide one a status for the time reported by
the rtc_get() function:
  0 - a reliable time is guaranteed,
< 0 - a reliable time isn't guaranteed (power fault, clock issues,
      and so on).

The RTC chip drivers are responsible for providing this info if the
corresponding chip supports such functionality. If not - always
report that the time is reliable.

The POST RTC test was modified to detect the RTC faults utilizing
this new rtc_get() feature.

Signed-off-by: Yuri Tikhonov <yur@emcraft.com>
diff --git a/drivers/rtc/ds174x.c b/drivers/rtc/ds174x.c
index 5f85a68..81a9cb3 100644
--- a/drivers/rtc/ds174x.c
+++ b/drivers/rtc/ds174x.c
@@ -65,7 +65,7 @@
 
 /* ------------------------------------------------------------------------- */
 
-void rtc_get( struct rtc_time *tmp )
+int rtc_get( struct rtc_time *tmp )
 {
 	uchar sec, min, hour;
 	uchar mday, wday, mon, year;
@@ -142,6 +142,8 @@
 
 	/* unlock clock registers after read */
 	rtc_write( RTC_CONTROLA, ( reg_a  & ~RTC_CA_WRITE ));
+
+	return 0;
 }
 
 void rtc_reset (void)