ubifs: fix possible dereference after free

mainline inclusion
from mainline-v6.7-rc1
commit d81efd66106c03771ffc8637855a6ec24caa6350
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8ZCT1

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d81efd66106c03771ffc8637855a6ec24caa6350



--------------------------------

'old_idx' could be dereferenced after free via 'rb_link_node' function
call.

Fixes: b5fda08e ("ubifs: Fix memleak when insert_old_idx() failed")
Co-developed-by: Ivanov Mikhail <ivanov.mikhail1@huawei-partners.com>
Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: ZhaoLong Wang <wangzhaolong1@huawei.com>