ring-buffer: Fix buffer locking in ring_buffer_subbuf_order_set()
In the Linux kernel, the following vulnerability has been resolved:

ring-buffer: Fix buffer locking in ring_buffer_subbuf_order_set()

Enlarge the critical section in ring_buffer_subbuf_order_set() to
ensure that error handling takes place with per-buffer mutex held,
thus preventing list corruption and other concurrency-related issues.