Fix the cb_break_lock spinlock in afs_volume struct by initialising it when
the volume record is allocated.

Also rename the lock to cb_v_break_lock to distinguish it from the lock of
the same name in the afs_server struct.

Without this, the following trace may be observed when a volume-break
callback is received:

  INFO: trying to register non-static key.
  the code is fine but needs lockdep annotation.
  turning off the locking correctness validator.
  CPU: 2 PID: 50 Comm: kworker/2:1 Not tainted 5.2.0-rc1-fscache+ #3045
  Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014
  Workqueue: afs SRXAFSCB_CallBack
  Call Trace:
   dump_stack+0x67/0x8e
   register_lock_class+0x23b/0x421
   ? check_usage_forwards+0x13c/0x13c
   __lock_acquire+0x89/0xf73
   lock_acquire+0x13b/0x166
   ? afs_break_callbacks+0x1b2/0x3dd
   _raw_write_lock+0x2c/0x36
   ? afs_break_callbacks+0x1b2/0x3dd
   afs_break_callbacks+0x1b2/0x3dd
   ? trace_event_raw_event_afs_server+0x61/0xac
   SRXAFSCB_CallBack+0x11f/0x16c
   process_one_work+0x2c5/0x4ee
   ? worker_thread+0x234/0x2ac
   worker_thread+0x1d8/0x2ac
   ? cancel_delayed_work_sync+0xf/0xf
   kthread+0x11f/0x127
   ? kthread_park+0x76/0x76
   ret_from_fork+0x24/0x30

Fixes: 68251f0a ("afs: Fix whole-volume callback handling")
Signed-off-by: David Howells <dhowells@redhat.com>