m_config: slightly simplify dynamic option initialization

We can assume memcpy is enough, because the source should be from
static data. (It wouldn't work if the data could contain pointers
back into itself.)

mpvcore/m_config.c

@@ -427,10 +427,9 @@ static struct m_config_option *m_config_add_option(struct m_config *config,
                         assert(0);
                 }
                 union m_option_value temp = {0};
-                m_option_copy(arg, &temp, co->data);
+                memcpy(&temp, co->data, arg->type->size);
                 memset(co->data, 0, arg->type->size);
                 m_option_copy(arg, co->data, &temp);
-                m_option_free(arg, &temp);
             }
         }
     }