py: Use mp_raise_TypeError/mp_raise_ValueError helpers where possible.

Saves 168 bytes on bare-arm.
diff --git a/py/objstringio.c b/py/objstringio.c
index 61a3075..88659de 100644
--- a/py/objstringio.c
+++ b/py/objstringio.c
@@ -39,7 +39,7 @@
 #if MICROPY_CPYTHON_COMPAT
 STATIC void check_stringio_is_open(const mp_obj_stringio_t *o) {
     if (o->vstr == NULL) {
-        mp_raise_msg(&mp_type_ValueError, "I/O operation on closed file");
+        mp_raise_ValueError("I/O operation on closed file");
     }
 }
 #else