make Ken happy

Reference: /n/sources/patch/applied/trap-clockintr
Date: Fri Jan  7 15:53:57 CET 2005

--- /sys/src/9/pc/trap.c	Fri Jan  7 15:53:57 2005
+++ /sys/src/9/pc/trap.c	Fri Jan  7 15:53:57 2005
@@ -313,6 +313,7 @@
 		cycles(&up->kentry);
 	}
 
+	clockintr = 0;
 	vno = ureg->trap;
 	if(ctl = vctl[vno]){
 		if(ctl->isintr){