IB/hfi1: Correctly move list in sc_disable()

Commit 13bac861 ("IB/hfi1: Fix abba locking issue with sc_disable()")
incorrectly tries to move a list from one list head to another.  The
result is a kernel crash.

The crash is triggered when a link goes down and there are waiters for a
send to complete.  The following signature is seen:

  BUG: kernel NULL pointer dereference, address: 0000000000000030
  [...]
  Call Trace:
   sc_disable+0x1ba/0x240 [hfi1]
   pio_freeze+0x3d/0x60 [hfi1]
   handle_freeze+0x27/0x1b0 [hfi1]
   process_one_work+0x1b0/0x380
   ? process_one_work+0x380/0x380
   worker_thread+0x30/0x360
   ? process_one_work+0x380/0x380
   kthread+0xd7/0x100
   ? kthread_complete_and_exit+0x20/0x20
   ret_from_fork+0x1f/0x30

The fix is to use the correct call to move the list.

Fixes: 13bac861 ("IB/hfi1: Fix abba locking issue with sc_disable()")
Signed-off-by: Dean Luick <dean.luick@cornelisnetworks.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Link: https://lore.kernel.org/r/166610327042.674422.6146908799669288976.stgit@awfm-02.cornelisnetworks.comSigned-off-by: Leon Romanovsky <leon@kernel.org>

drivers/infiniband/hw/hfi1/pio.c

@@ -913,8 +913,7 @@ void sc_disable(struct send_context *sc)
 	spin_unlock(&sc->release_lock);
 
 	write_seqlock(&sc->waitlock);
-	if (!list_empty(&sc->piowait))
-		list_move(&sc->piowait, &wake_list);
+	list_splice_init(&sc->piowait, &wake_list);
 	write_sequnlock(&sc->waitlock);
 	while (!list_empty(&wake_list)) {
 		struct iowait *wait;