mm: eliminate "expecting prototype" kernel-doc warnings

Fix stray kernel-doc warnings in mm/ due to mis-typed or missing function
names.

Quietens these kernel-doc warnings:

  mm/mmu_gather.c:264: warning: expecting prototype for tlb_gather_mmu(). Prototype was for __tlb_gather_mmu() instead
  mm/oom_kill.c:180: warning: expecting prototype for Check whether unreclaimable slab amount is greater than(). Prototype was for should_dump_unreclaim_slab() instead
  mm/shuffle.c:155: warning: expecting prototype for shuffle_free_memory(). Prototype was for __shuffle_free_memory() instead

Link: https://lkml.kernel.org/r/20210411210642.11362-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/shuffle.c b/mm/shuffle.c
index 9c2e145..c13c33b 100644
--- a/mm/shuffle.c
+++ b/mm/shuffle.c
@@ -147,8 +147,8 @@ void __meminit __shuffle_zone(struct zone *z)
 	spin_unlock_irqrestore(&z->lock, flags);
 }
 
-/**
- * shuffle_free_memory - reduce the predictability of the page allocator
+/*
+ * __shuffle_free_memory - reduce the predictability of the page allocator
  * @pgdat: node page data
  */
 void __meminit __shuffle_free_memory(pg_data_t *pgdat)