[FIXUP/OFW] Increase append child node's ref_count

rt_ofw_append_child append a new child node and return,
ref_get is necessary.

Signed-off-by: GuEe-GUI <2991707448@qq.com>

components/drivers/ofw/base.c

@@ -1412,7 +1412,7 @@ struct rt_ofw_node *rt_ofw_append_child(struct rt_ofw_node *parent, const char *
         }
     }
 
-    return np;
+    return rt_ofw_node_get(np);
 }
 
 rt_err_t rt_ofw_append_prop(struct rt_ofw_node *np, const char *name, int length, void *value)