DOC: Fix wrong identifier name in Documentation/driver-model/devres.txt

Above and below we talk about my_midlayer_create_something, I assume that is
also meant here.

Signed-off-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>