CVE-2025-38621 md: make rdev_addable usable for rcu mode

In the Linux kernel, the following vulnerability has been resolved: md: make rdevaddable usable for rcu mode Our testcase trigger panic: BUG: kernel NULL pointer dereference, address: 00000000000000e0 ... Oops: Oops: 0000 1 SMP NOPTI CPU: 2 UID: 0 PID: 85 Comm: kworker/2:1 Not tainted 6.16.0+ 94...