fix "clock changes underfoot" warning.

Reference: /n/atom/patch/applied/rtcfix
Date: Fri Apr  4 05:04:48 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/devrtc.c	Fri Apr  4 05:04:16 2014
+++ /sys/src/nix/k10/devrtc.c	Fri Apr  4 05:04:16 2014
@@ -162,7 +162,8 @@
 	ot = 0;
 	t = rtcextract();
 	for(i = 0; i < 100; i++){
-		ot = rtcextract();
+		ot = t;
+		t = rtcextract();
 		if(ot == t)
 			break;
 	}