of: unittest: fix use-after-free in of_unittest_changeset()

In the Linux kernel, the following vulnerability has been resolved:

of: unittest: fix use-after-free in of_unittest_changeset()

The variable 'parent' is assigned the value of 'nchangeset' earlier in the

function, meaning both point to the same struct device_node. The call to

of_node_put(nchangeset) can decrement the reference count to zero and

free the node if there are no other holders. After that, the code still

uses 'parent' to check for the presence of a property and to read a

string property, leading to a use-after-free.

Fix this by moving the of_node_put() call after the last access to

'parent', avoiding the UAF.