test: fix build (update for new error message)

R=golang-dev
CC=golang-dev
https://golang.org/cl/13521044

test/syntax/chan1.go

@@ -10,8 +10,8 @@ var c chan int
 var v int
 
 func main() {
-	if c <- v { // ERROR "send statement.*value.*select"
+	if c <- v { // ERROR "used as value"
 	}
 }
 
-var _ = c <- v // ERROR "send statement.*value.*select"
+var _ = c <- v // ERROR "used as value"