Add missing devm_request_free_mem_region() to devres.rst.
It's introduced by commit 0092908d ("mm: factor out a
devm_request_free_mem_region helper").
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220927080215.1359979-1-yangyingliang@huawei.comSigned-off-by: NJonathan Corbet <corbet@lwn.net>