go.tools/go/types: fix build

(I inadvertently submitted a modified file.)

R=adonovan
CC=golang-dev
https://golang.org/cl/22750044

go/types/testdata/stmt0.src

@@ -53,7 +53,7 @@ func assignments1() {
 
 	f -= 1
 	f /= 0
-	f = float32(1.0)/0
+	f = float32(0)/0 /* ERROR "division by zero" */
 	f -= "foo" /* ERROR "cannot convert.*float64" */
 
 	c *= 1