mm/hwpoison: replace atomic_long_sub() with atomic_long_dec()

Replace atomic_long_sub() with atomic_long_dec() since the page is normal
page instead of hugetlbfs page or thp.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 32351ec..c69217c 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1366,7 +1366,7 @@
 			return 0;
 		}
 		if (TestClearPageHWPoison(p))
-			atomic_long_sub(nr_pages, &num_poisoned_pages);
+			atomic_long_dec(&num_poisoned_pages);
 		pr_info("MCE: Software-unpoisoned free page %#lx\n", pfn);
 		return 0;
 	}