mm: add lockdep annotation to pgdat_init_all_done_comp completer

Add the missing lockdep annotation to avoid this kernel warning:

 smp: Brought up 1 node, 1 CPU
 INFO: trying to register non-static key.
 The code is fine but needs lockdep annotation, or maybe
 you didn't initialize this object before use?'
 turning off the locking correctness validator.
 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc5+ torvalds#683
 Hardware name: 9000/785/C3700
 Backtrace:
  [<000000004030bcd0>] show_stack+0x74/0xb0
  [<000000004146c63c>] dump_stack_lvl+0x104/0x180
  [<000000004146c6ec>] dump_stack+0x34/0x48
  [<000000004040e5b4>] register_lock_class+0xd24/0xd30
  [<000000004040c21c>] __lock_acquire.isra.0+0xb4/0xac8
  [<000000004040cd60>] lock_acquire+0x130/0x298
  [<000000004147095c>] _raw_spin_lock_irq+0x60/0xb8
  [<0000000041474a4c>] wait_for_completion+0xa0/0x2d0
  [<000000004012bf04>] page_alloc_init_late+0xf8/0x2b0
  [<0000000040102b20>] kernel_init_freeable+0x464/0x7f0
  [<000000004146df68>] kernel_init+0x64/0x3a8
  [<0000000040302020>] ret_from_kernel_thread+0x20/0x28

Link: https://lkml.kernel.org/r/ZNZce1KGxP1dxpTN@p100
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mm_init.c

@@ -2377,6 +2377,7 @@ void __init page_alloc_init_late(void)
 	int nid;
 
 #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
+	init_completion(&pgdat_init_all_done_comp);
 
 	/* There will be num_node_state(N_MEMORY) threads */
 	atomic_set(&pgdat_init_n_undone, num_node_state(N_MEMORY));