hwclock: make it report system/rtc clock difference

function                                             old     new   delta
rtc_tm2time                                            -      89     +89
read_rtc                                              23      86     +63
rtc_read_tm                                            -      49     +49
hwclock_main                                         428     466     +38
rtcwake_main                                         453     477     +24
rtc_read_time                                        142       -    -142
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 3/0 up/down: 263/-142)          Total: 121 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/util-linux/rtcwake.c b/util-linux/rtcwake.c
index 049f699..64c3e7e 100644
--- a/util-linux/rtcwake.c
+++ b/util-linux/rtcwake.c
@@ -160,7 +160,12 @@
 
 	/* relative or absolute alarm time, normalized to time_t */
 	sys_time = time(NULL);
-	rtc_time = rtc_read_time(fd, utc);
+	{
+		struct tm tm;
+		rtc_read_tm(&tm, fd);
+		rtc_time = rtc_tm2time(&tm, utc);
+	}
+
 
 	if (alarm_time) {
 		if (alarm_time < sys_time)