zephyr: Update for refactored zephyr device structures.

Updates the zephyr port to use refactored device structures introduced in
zephyr 2.3.

ports/zephyr/machine_i2c.c

@@ -48,7 +48,7 @@ typedef struct _machine_hard_i2c_obj_t {
 
 STATIC void machine_hard_i2c_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
     machine_hard_i2c_obj_t *self = self_in;
-    mp_printf(print, "%s", self->dev->config->name);
+    mp_printf(print, "%s", self->dev->name);
 }
 
 mp_obj_t machine_hard_i2c_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *all_args) {