fix compiler warnings

src/qbe/gvn.c

@@ -43,11 +43,11 @@ static uint gvntbln;
 static Ins *
 gvndup(Ins *i, int insert)
 {
-	uint idx, n;
+	uint idx;
 	Ins *ii;
 
 	idx = ihash(i) % gvntbln;
-	for (n=1;; n++) {
+	for (;;) {
 		ii = gvntbl[idx];
 		if (!ii)
 			break;