Use MP_ROM_QSTR

There are more exeptions scattered across the codebase, but this is the
only one that foiled my attempts to use grep to check that every object
using default___exit___obj also had a deinit method.

Author: jepler

shared-bindings/analogio/AnalogOut.c

@@ -100,7 +100,7 @@ MP_PROPERTY_GETSET(analogio_analogout_value_obj,
 
 static const mp_rom_map_elem_t analogio_analogout_locals_dict_table[] = {
     // instance methods
-    { MP_OBJ_NEW_QSTR(MP_QSTR_deinit), MP_ROM_PTR(&analogio_analogout_deinit_obj) },
+    { MP_ROM_QSTR(MP_QSTR_deinit), MP_ROM_PTR(&analogio_analogout_deinit_obj) },
     { MP_ROM_QSTR(MP_QSTR___enter__),  MP_ROM_PTR(&default___enter___obj) },
     { MP_ROM_QSTR(MP_QSTR___exit__),   MP_ROM_PTR(&default___exit___obj) },