kunit: fix reference count leak in kfree_at_end

The reference counting issue happens in the normal path of
kfree_at_end(). When kunit_alloc_and_get_resource() is invoked, the
function forgets to handle the returned resource object, whose refcount
increased inside, causing a refcount leak.

Fix this issue by calling kunit_alloc_resource() instead of
kunit_alloc_and_get_resource().

Fixed the following when applying:
Shuah Khan <skhan@linuxfoundation.org>

CHECK: Alignment should match open parenthesis
+	kunit_alloc_resource(test, NULL, kfree_res_free, GFP_KERNEL,
 				     (void *)to_free);

Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Reviewed-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>