lib/test: use after free in register_test_dev_kmod()

The "test_dev" pointer is freed but then returned to the caller.

Fixes: d9c6a72d ("kmod: add test driver to stress test the module loader")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>