Documentation: devres: add missing IO helper

Add missing devm_request_free_mem_region() to devres.rst.
It's introduced by commit 0092908 ("mm: factor out a
devm_request_free_mem_region helper").

Signed-off-by: Yang Yingliang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Corbet <[email protected]>

Author: Yang Yingliang

Documentation/driver-api/driver-model/devres.rst

@@ -301,6 +301,7 @@ IO region
   devm_release_region()
   devm_release_resource()
   devm_request_mem_region()
+  devm_request_free_mem_region()
   devm_request_region()
   devm_request_resource()