cmd/compiler/internal/gc: fix argument for Sprintf

Val.Ctype used to be struct field, it's now a method.

Change-Id: I08f0b32b66dba15b2a392e84a557efb905b530cb
Reviewed-on: https://go-review.googlesource.com/14031Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/fmt.go

@@ -356,7 +356,7 @@ func Vconv(v Val, flag int) string {
 		return "nil"
 	}
 
-	return fmt.Sprintf("<ctype=%d>", v.Ctype)
+	return fmt.Sprintf("<ctype=%d>", v.Ctype())
 }
 
 /*