Change mp_obj_type_t.name from const char * to qstr.

Ultimately all static strings should be qstr.  This entry in the type
structure is only used for printing error messages (to tell the type of
the bad argument), and printing objects that don't supply a .print method.
diff --git a/py/objarray.c b/py/objarray.c
index d1bc08b..4a70f9f 100644
--- a/py/objarray.c
+++ b/py/objarray.c
@@ -161,7 +161,7 @@
 
 const mp_obj_type_t array_type = {
     { &mp_const_type },
-    "array",
+    .name = MP_QSTR_array,
     .print = array_print,
     .make_new = array_make_new,
     .getiter = array_iterator_new,
@@ -223,7 +223,7 @@
 
 STATIC const mp_obj_type_t array_it_type = {
     { &mp_const_type },
-    "array_iterator",
+    .name = MP_QSTR_iterator,
     .iternext = array_it_iternext,
 };