simplify and remove case where callhzclock could be set without hzclock being called

Reference: /n/atom/patch/applied/timerintersimple
Date: Thu Mar 27 07:14:17 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/port/portclock.c	Thu Mar 27 07:14:12 2014
+++ /sys/src/nix/port/portclock.c	Thu Mar 27 07:14:13 2014
@@ -197,10 +197,7 @@
 		when = t->twhen;
 		if(when > now){
 			timerset(when);
-			iunlock(tt);
-			if(callhzclock)
-				hzclock(u);
-			return;
+			break;
 		}
 		tt->head = t->tnext;
 		assert(t->tt == tt);
@@ -209,12 +206,14 @@
 		if(t->tf)
 			(*t->tf)(u, t);
 		else
-			callhzclock++;
+			callhzclock = 1;
 		ilock(tt);
 		if(t->tmode == Tperiodic)
 			tadd(tt, t);
 	}
 	iunlock(tt);
+	if(callhzclock)
+		hzclock(u);
 }
 
 void