That commit triggered a new WARN when unloading the module (see at the
end of the commit message). When a class_dev is embedded in a structure
then that class_dev is the thing that controls the lifetime of that
structure, for that reason device managed allocations can't be used here.
See Documentation/kobject.txt.
Revert the above patch, so the struct is allocated using kzalloc and we
have a release function for it that frees the allocated memory, otherwise
it is broken.