ksm: use the helper method to do the hlist_empty check

This just uses the helper function to cleanup the assumption on the
hlist_node internals.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Petr Holasek <pholasek@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/ksm.c

@@ -625,7 +625,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
 		unlock_page(page);
 		put_page(page);
 
-		if (stable_node->hlist.first)
+		if (!hlist_empty(&stable_node->hlist))
 			ksm_pages_sharing--;
 		else
 			ksm_pages_shared--;